JPH11122818A - System interconnector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make efficiency higher, and to prevent an output current from flowing reversely, by detecting a system voltage or the output current of an inverter circuit varying the boosted voltage of a booster circuit on its basis, and reducing power loss caused by the booster circuit. SOLUTION: A system interconnector 2 which supplies AC power from an inverter circuit 6 to a load and interconnects with a lower system, is provided with a booster circuit 5 which boosts a DC voltage from a DC power source, and an inverter circuit 6 which converts a DC from the booster circuit 5 into an AC. And the system voltage or the output current of the inverter circuit 6 are detected, and the boosted voltage of the booster circuit 5 is varied on the basis of it. Consequently, it becomes possible to vary the boosted voltage in accordance with the variation of the system voltage, or to make the boosted voltage higher, when the difference between the boosted voltage and the system voltage becomes smaller by the variation of the system voltage, and a peak is generated in the output current. Accordingly, it becomes possible to reduce power loss caused by unnecessary boosting, and to prevent the output current of the inverter circuit from flowing reversely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system interconnection device for interconnecting a distributed power source such as a photovoltaic power generation and an electric power system.

[0002]

2. Description of the Related Art In recent years, a photovoltaic power generation system has been proposed in which a distributed power supply using a photovoltaic power generation and a commercial power supply are interconnected, and when the power cannot be provided by the distributed power supply alone, the power is supplied from the grid side. The system is being developed.

[0003] Figure 5 is a schematic configuration diagram of a photovoltaic system, reference numeral 1 denotes a solar battery as a DC power source, 2 ₀ grid interconnection device, a so-called, a power conditioner, the system interconnection device 2 _0, the solar cell 1
, A booster circuit 5 for boosting the DC voltage to a constant voltage, an inverter circuit 6 for converting the DC power from the booster circuit 5 into AC power synchronized with the system power supply 4, and a filter circuit including a coil L and a capacitor C 7 and current sensor 8
On the basis of the output current of the inverter circuit 6 detected by the output current detection circuit 9, the system voltage detected by the system voltage detection circuit 10, and the current command from the current command circuit 11 via the inverter drive circuit 12. A current control circuit 13 for controlling an output current of the inverter circuit 6,
While detecting an abnormality on the system side such as a power failure, the switch 15 is opened via the relay drive circuit 14 to disconnect from the system,
System protection relay 1 for stopping drive of inverter circuit 6
6, and the boosted voltage detected by the boosted voltage detection circuit 18 is
A boost voltage control circuit 21 controls the boost circuit 5 via the boost drive circuit 20 so that the boost voltage is set by the boost voltage setting circuit 32. In addition, 3 is a load.

[0004]

However, in such a conventional example, the boosted voltage of the booster circuit 5 is changed to a high voltage value with a margin slightly higher than the peak value of the system voltage in consideration of the fluctuation of the system voltage. When the system voltage is low, the boosted voltage becomes unnecessarily high, and the booster circuit 5 wastefully consumes electric energy, thereby lowering the efficiency.

Therefore, it is conceivable to set the boosted voltage low. However, if the boosted voltage is too low, the difference between the boosted voltage V1 and the system voltage V2 becomes small as shown in FIG. As shown in b), when a distortion (peak) occurs in the output current I and the system voltage V2 exceeds the boosted voltage V1, the output current I flows backward.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in view of the above circumstances. Therefore, there is provided a system interconnection device which reduces power loss due to a booster circuit to increase efficiency and prevents output current from flowing back. The purpose is to provide.

[0007]

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

[0008] That is, a system interconnection device of the present invention according to claim 1 includes a booster circuit for boosting a DC voltage from a DC power supply;
An inverter circuit for converting DC from a booster circuit to AC, and supplying AC power from the inverter circuit to a load, and a system interconnection device for interconnecting the power system with a system voltage or an output of the inverter circuit. The current is detected, and the boosted voltage of the booster circuit is varied based on the detected current.

According to a second aspect of the present invention, in the configuration of the first aspect, a system voltage detecting circuit for detecting a system voltage and a boosted voltage of the boosting circuit based on an output of the system voltage detecting circuit. And a step-up voltage varying means for varying the voltage.

According to a third aspect of the present invention, in the configuration of the first aspect, a peak current detecting means for detecting a peak of the output current of the inverter circuit and an output of the peak current detecting means. And a boost voltage varying means for varying a boost voltage of the boost circuit.

According to a fourth aspect of the present invention, in the configuration of the third aspect, the peak current detecting means detects a peak value of a fundamental wave of the output current and a peak value of the output current. The boosted voltage varying means varies the boosted voltage based on a difference between the two peak values.

According to a fifth aspect of the present invention, there is provided a system interconnection device according to the first aspect, wherein current distortion detecting means for detecting distortion of an output current of the inverter circuit, and an output of the current distortion detecting means. And a boost voltage varying means for varying the boost voltage of the boost circuit.

According to the first aspect of the present invention, since the system voltage or the output current of the inverter circuit is detected and the boosted voltage of the booster circuit is varied based on the detected system voltage or the output current of the inverter circuit,
The boosted voltage can be varied in accordance with the system voltage fluctuation, or if the difference between the boosted voltage and the system voltage becomes small due to the system voltage fluctuation and a distortion (peak) occurs in the output current, the boosting is performed. The voltage can be increased, thereby reducing the power loss due to unnecessary boosting to increase the efficiency and preventing the output current of the inverter circuit from flowing backward due to the boosted voltage being too low. Become.

According to a second aspect of the present invention, there is provided a system voltage detecting circuit for detecting a system voltage, and a boosted voltage variable for changing a boosted voltage of a boosting circuit based on an output of the system voltage detecting circuit. Means, the boosted voltage can be varied according to the fluctuation of the system voltage, whereby the power loss due to unnecessary boosting can be reduced and the efficiency can be increased. Is too low, the output current of the inverter circuit can be prevented from being distorted or flowing backward.

According to a third aspect of the present invention, there is provided a peak current detecting means for detecting a peak of an output current of an inverter circuit, and a boosted voltage of a boosting circuit based on an output of the peak current detecting means. Since there is provided a variable step-up voltage varying means, the difference between the step-up voltage and the system voltage is reduced due to the fluctuation of the system voltage, and the output current is distorted (peak).
In the case where the voltage rise occurs, the distortion and the backflow of the output current can be prevented by increasing the boosted voltage, while the power loss due to unnecessary boosting can be reduced and the efficiency can be increased. According to the system interconnection device of No. 4, by changing the boosted voltage based on the difference between the peak value of the fundamental wave of the output current and the peak value of the output current, the peak can be surely obtained regardless of the magnitude of the output current. It is possible to detect and change the boosted voltage.

According to a fifth aspect of the present invention, a current distortion detecting means for detecting a distortion of an output current of the inverter circuit, and a booster of the booster circuit based on an output of the current distortion detecting means. Since there is provided a boosted voltage varying means for varying the voltage, when the difference between the boosted voltage and the system voltage is reduced due to the fluctuation of the system voltage and the output current is distorted,
By increasing the boosted voltage, the distortion and the backflow of the output current can be prevented, while the power loss due to unnecessary boosting can be reduced and the efficiency can be increased.

[0017]

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

(Embodiment 1) FIG. 1 is a schematic configuration diagram of a photovoltaic power generation system according to the present invention.

In this embodiment, a system in which a distributed power source using solar power generation and a commercial power source are interconnected and the power is supplied from the grid side when the power cannot be provided by the distributed power source alone. The same reference numerals are given to portions corresponding to the conventional example in FIG.

This system includes a solar cell 1 as a DC power supply and a system interconnection device 2 according to the present invention.
The DC power from the solar cell 1 is converted into AC power to load 3
And is connected to the power system of the system power supply 4.

The grid interconnection device 2 of this embodiment is a so-called power conditioner, and includes a booster circuit 5 for boosting a DC voltage from the solar cell 1 as described later, and a DC power from the booster circuit 5. Circuit 6 which converts AC power into AC power synchronized with the system power supply 4, a filter circuit 7 including a coil L and a capacitor C, and a current sensor 8
On the basis of the output current of the inverter circuit 6 detected by the output current detection circuit 9, the system voltage detected by the system voltage detection circuit 10, and the current command from the current command circuit 11 via the inverter drive circuit 12. A current control circuit 13 for controlling an output current of the inverter circuit 6,
While detecting an abnormality on the system side such as a power failure, the switch 15 is opened via the relay drive circuit 14 to disconnect from the system,
System protection relay 1 for stopping drive of inverter circuit 6
6 and a boost voltage varying means 17 for varying the boost voltage of the boost circuit 5 based on the system voltage detected by the system voltage detection circuit 10 as described later.

The boost voltage variable means 17 includes a boost voltage detection circuit 18 for detecting a boost voltage, and a boost voltage command value calculation circuit 19 for calculating and instructing a target boost voltage command value based on the detected system voltage. And a boost voltage control circuit 21 for controlling the boost circuit 5 via the boost drive circuit 20 so that the boost voltage command value is obtained.

In this embodiment, the boosted voltage of the booster circuit 5 is set to the minimum necessary voltage to increase the efficiency, and the difference between the boosted voltage and the system voltage is reduced due to the fluctuation of the system voltage, so that the output current is distorted (peak). ) Or the backflow of the output current, the boosted voltage varying means 17 varies the boosted voltage in accordance with the system voltage detected by the system voltage detection circuit 10.

That is, the boosted voltage command value calculation circuit 19 of the boosted voltage variable means 17 _adds the predetermined constant value ΔV to the system voltage VUV between UVs detected by the system voltage detection circuit 10.
_The value obtained by adding _DD is referred to as a boost voltage command value V _DDref (= V _UV + Δ
V _DD ) to the boosted voltage control circuit 21, and the boosted voltage control circuit 21 detects the boosted voltage V _DD
Is controlled so as to match the boosted voltage command value V _DDref , whereby the boosted voltage is controlled to a voltage higher by a certain value than the system voltage in accordance with the fluctuation of the system voltage. Become. This constant value ΔV _DD is a minimum value that can prevent, for example, distortion (peak) from occurring in the output current or backflow of the output current.

Therefore, according to this embodiment, the boosted voltage by the booster circuit 5 needs to be free from distortion (peak) in the output current and backflow of the output current regardless of the fluctuation of the system voltage. Since the minimum voltage is used, the power loss by the booster circuit 5 is reduced and the efficiency is improved.

It is to be noted that the constant value ΔV _DD may be higher than the minimum required value. In other words, the constant value ΔV _DD is a value that prevents the backflow of the output current and increases the efficiency as compared with the conventional example. Good.

As another embodiment of the present invention, the boosted voltage command value calculating circuit 19 _adds a predetermined constant value K (≧) to the system voltage VUV between UVs detected by the system voltage detecting circuit 10. 1) is multiplied by the boost voltage command value V _DDref (=
_K.V.sub.UV ) may be provided to the boost voltage control circuit 21. This constant value K is determined in the same manner as in the above-described embodiment.

(Embodiment 2) FIG. 2 is a schematic configuration diagram of a photovoltaic power generation system according to another embodiment of the present invention, in which parts corresponding to the above-described embodiments have the same reference numerals. Attach.

In the above-described embodiment, the system voltage is detected and the boosted voltage is controlled to the optimum voltage, thereby improving the efficiency and preventing the output current from flowing backward. Instead of the voltage, a peak of the output current is detected, and the boosted voltage is controlled based on the detected peak.

That is, in this embodiment, the peak current detecting means 22 for detecting the peak of the output current of the inverter circuit 6, and the boosted voltage of the boosting circuit 5 is varied based on the output of the peak current detecting means 22. and a boosted voltage varying means 17 _1.

The peak current detecting means 22 includes a fundamental wave peak detecting circuit 23 for detecting the peak value of the fundamental wave of the output current detected by the output current detecting circuit 9, and an output current peak detecting circuit for detecting the peak value of the output current. Circuit 24, the fundamental wave peak detection circuit 23 includes a band-pass filter that passes the fundamental wave, and a peak hold circuit that holds the peak of the fundamental wave. The output current peak detection circuit 24 includes: A peak hold circuit for holding the peak of the output current is provided.

The boosted voltage varying means 17 _1, the boosted voltage detecting circuit 18 for detecting the boosted voltage, the peak value of the output current from the peak value of the fundamental wave and the output current peak detection circuit 24 from the fundamental wave peak detection circuit 23 Comparison circuit 2 for comparing
5, on the basis of a comparison result of the comparison circuit 25, a boost voltage command value calculating circuit 19 ₁ for calculating command the boost voltage command value as a target, through the step-up driver circuit 20 so that the boost voltage command value A boost voltage control circuit 21 for controlling the boost circuit 5;

The comparison circuit 25 compares the two peak values to determine whether or not the peak value of the output current has exceeded the peak value of the fundamental wave by a predetermined level or more, and provides a corresponding output. Things. As described above, when the difference between the boosted voltage and the system voltage is reduced and the output current is distorted (peak) as shown in FIG. 6B, the peak value of the output current is changed to the fundamental wave (distortion of the distortion). Since the peak value of the output current exceeds the peak value of the fundamental wave, that is, when the distortion of the output current exceeds the predetermined level, that is, the peak value of the output current exceeds the predetermined level of the fundamental wave. when increased Te, comparator circuit 25 is to provide a corresponding output to the boost voltage command value calculating circuit 19 _1.

The boost voltage command value calculating circuit 19 _1, the peak value of the output current, when the increased beyond a predetermined level than the peak value of the fundamental wave based on the output of the comparator circuit 25, the boosted voltage The command value V _DDref is added with a predetermined constant value ΔV _DD to give a new boost voltage command value V _DDref to the boost voltage control circuit 21. The peak value of the output current does not exceed the predetermined level. When the number of times is a predetermined number of times, it is determined that the boosted voltage remains sufficiently higher than the system voltage, and a predetermined constant value ΔV _DD is subtracted from the boosted voltage command value V _DDref to obtain a new boosted voltage. As the command value V _DDref , the boost voltage control circuit 21
In addition, the peak value of the output current is
If the predetermined level is not _exceeded and the number of times does not continue for a predetermined number of times, it is determined that the boosted voltage is not high enough to be reduced, and the boosted voltage command value V _DDref is _left as it is.

FIG. 3 is a flowchart of the above- _described calculation of the boost voltage command value V _DDref . First, the peak value (i _op ) of the fundamental wave of the output current is detected (step n1), and the peak value (i) of the output current is detected. _p ) is detected (step n2), and the peak value of the output current is set to a predetermined constant a as the peak value of the fundamental wave.
It is determined whether the value (a · i _op) or multiplied by (Step n3), when it is the multiplied value above, the boost voltage command value V _DDREF as distortion is caused in the output current
, A predetermined constant value ΔV _DD (> 0) is added _thereto , and the process returns to step n1 as a new boosted voltage command value V _DDref (step n4).

In step n3, if the peak value of the output current is not greater than the value obtained by multiplying the peak value of the fundamental wave by a predetermined constant a, it is determined whether the boosted voltage command value V _DDref is the same for a predetermined number of times. (Step n)
5) If not the same, it is determined that the boosted voltage is not high enough to be reduced, and the process returns to step n1 with the boosted voltage command value V _DDref as it is (step n6).

In step n5, when the boosted voltage command value V _DDref is the same continuously for a predetermined number of times,
_Assuming that the boosted voltage is sufficiently higher than the system voltage, a predetermined constant value ΔV _DD is subtracted from the boosted voltage command value V _DDref to return to step n1 as a new boosted voltage command value V _DDref (step n7).

The boosted voltage control circuit 21 controls the detected boosted voltage V _DD so as to match the boosted voltage command value V _DDref calculated as described above. If the distortion (peak) occurs in the output current, the boost voltage is immediately increased to eliminate the distortion of the output current. If the boost voltage remains sufficiently higher than the system voltage, the boost voltage is reduced and optimized. Voltage can be suppressed.

Therefore, according to this embodiment,
The boosted voltage by the booster circuit 5 is a minimum necessary voltage that does not increase the distortion (peak) of the output current or cause the output current to flow backward regardless of the fluctuation of the system voltage. 5 is reduced, and the efficiency is improved.

Further, in this embodiment, since the boosted voltage is varied based on the ratio between the peak value of the fundamental wave of the output current and the peak value of the output current, the peak can be reliably determined regardless of the magnitude of the output current. Can be detected.

(Embodiment 3) FIG. 4 is a schematic configuration diagram of a photovoltaic power generation system according to still another embodiment of the present invention, and portions corresponding to the embodiment of FIG. Assign a sign.

In the above-described embodiment, the peak of the output current is detected, and the boosted voltage is controlled based on the peak. However, in this embodiment, the distortion of the output current is detected, and the boosted voltage is detected based on the detected distortion. It is configured to control.

That is, in this embodiment, the current distortion detecting means 26 for detecting the distortion of the output current of the inverter circuit 6
If, based on the output of the current distortion detection means 26, and a boosted voltage varying means 17 ₂ for varying the boost voltage of the booster circuit 5.

The current distortion detecting means 26 includes a band-pass filter 27 that passes only the fundamental wave of the output current detected by the output current detecting circuit 9, and a first Fourier transform for fast- Fourier transforming the output of the band-pass filter 27. A fast Fourier transform circuit (FFT) 28, a second fast Fourier transform circuit (FFT) 29 for fast Fourier transforming the output current, and an output of the second fast Fourier transform circuit 29, for example, from the first to fifth order Maximum value circuit 3 for extracting the maximum harmonic component
0.

The boosted voltage varying means 17 ₂ includes a boost voltage detection circuit 18 for detecting the boosted voltage, comparator circuit 31 for comparing the outputs of the maximum value (MAX) circuit 30 of the first fast Fourier transform circuit 28 If, based on the comparison result of the comparison circuit 31, a boost voltage command value calculating circuit 19 ₂ for calculating command the boost voltage command value as a target, through the step-up driver circuit 20 so that the boost voltage command value boost And a boost voltage control circuit 21 for controlling the circuit 5.

The comparison circuit 31 compares the output of the maximum value circuit 30 with the output of the first fast Fourier transform circuit 28, and when the difference exceeds a predetermined level, that is, a predetermined output current. when the level or more strain has occurred is to provide a corresponding output to the boost voltage command value calculating circuit 19 _2.

The boost voltage command value calculating circuit 19 ₂ is a similar embodiment to embodiment basically described above, when the increased beyond the level at which distortion of the output current is determined in advance, the output of the comparison circuit 31 Based on the boost voltage command value V _DDref ,
A predetermined constant value ΔV _DD is added to the boosted voltage control circuit 21 as a new boosted voltage command value V _DDref , and the distortion of the output current does not exceed the predetermined level.
When the boosted voltage command value V has reached a predetermined number of times, it is determined that the boosted voltage continues to be sufficiently higher than the system voltage.
_The predetermined constant value ΔV _DD is subtracted from _DDref and given as a new boosted voltage command value V _DDref to the boosted voltage control circuit 21. Further, the number of times that the distortion of the output current does not exceed the predetermined level and However, when the predetermined number of times is not continuous, the boosted voltage is not high enough to be reduced, and the boosted voltage command value V _DDref is _left as it is.

Therefore, according to the present embodiment, the boosted voltage by the booster circuit 5 is at least the minimum necessary for preventing the distortion of the output current or the backflow of the output current regardless of the fluctuation of the system voltage. , The power loss by the booster circuit 5 is reduced, and the efficiency is improved.

(Other Embodiments) As another embodiment of the present invention, the above embodiments may be combined. For example, a command value of a boosted voltage is calculated from a system voltage,
After reaching the command value, the command value of the boosted voltage may be calculated based on the peak of the output current.

Although the above embodiment has been described by applying the present invention to a solar power generation system using a solar cell as a DC power supply, the present invention is not limited to the solar power generation system, but may be applied to another distributed power supply such as a fuel cell. It may be applied to a system.

[0051]

As described above, according to the present invention, the system voltage or the output current is detected, and the boost voltage is varied based on the detected system voltage or output current. Therefore, the boost voltage can be varied according to the fluctuation of the system voltage. As a result, the power loss due to unnecessary boosting can be reduced and the efficiency can be improved, while preventing the output current from flowing backward due to the boosted voltage being too low.

[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 a solar power generation system according to another embodiment of the present invention.

FIG. 3 is a flowchart of a boost command value calculation.

FIG. 4 is a configuration diagram of a solar power generation system according to still another embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional example.

FIG. 6 is a waveform chart for explaining a problem of the conventional example.

[Explanation of symbols]

1 the solar cells 2 _1, 2 ₂ grid interconnection device 3 load 4 the system power supply 5 booster circuit 6 inverter circuit 10 the system voltage detecting circuit 17 _1, 17 ₂ boosted voltage varying means 22 peak current detection means 26 current distortion detection means

Claims (5)

[Claims] 1. A power supply system comprising: a booster circuit for boosting a DC voltage from a DC power supply; and an inverter circuit for converting DC from the booster circuit to AC, and supplying AC power from the inverter circuit to a load. A system interconnection device that detects a system voltage or an output current of the inverter circuit and varies a boosted voltage of the booster circuit based on the detected system voltage or the output current of the inverter circuit. 2. The system interconnection according to claim 1, further comprising: a system voltage detection circuit for detecting a system voltage; and a boost voltage variable means for varying a boost voltage of the boost circuit based on an output of the system voltage detection circuit. apparatus. 3. A power supply system comprising: a peak current detecting means for detecting a peak of an output current of the inverter circuit; and a boosted voltage varying means for varying a boosted voltage of the boosting circuit based on an output of the peak current detecting means. Item 6. The system interconnection device according to Item 1. 4. The peak current detecting means detects a peak value of a fundamental wave of the output current and a peak value of the output current, and the boosted voltage varying means detects a difference between the two peak values. 4. The system interconnection device according to claim 3, wherein the step-up voltage is varied based on the voltage. 5. A current distortion detecting means for detecting a distortion of an output current of the inverter circuit, and a boost voltage varying means for varying a boost voltage of the boost circuit based on an output of the current distortion detecting means. Item 6. The system interconnection device according to Item 1.