JP2003189475A - System linked power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system linked power converter in which a plurality of self-exciting single phase inverters are directly connected in series to each other, while DC circuit thereof are independent from each other to realize multiple outputs, connected to an AC power system via reactors, and which does not need a multiplex transformer for realizing a DC multiplex system. <P>SOLUTION: A first system linked power converter 1 includes a power converting circuit 2 including self-exciting single phase inverters connected in series to each other, a switching pulse supply unit 3 which generates and supplies switching pulse signals, an apparatus loss detection unit 4 which detects DC output voltages of smoothing capacitors constituting the single phase AC inverters in the power converting circuit 2 and calculates the apparatus losses according to the detected output voltages, and an output voltage control unit 5 which controls the output voltages of the single phase AC inverters in the power converting circuit 2 according to the calculation results. The respective outputs of the power converting unit 2 are connected to respective phases of a three-phase AC power system Vs via reactors L1-L3. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid interconnection power converter for compensating reactive power in an AC power grid.

[0002]

2. Description of the Related Art Conventionally, as a system interconnection power converter for compensating reactive power of a power system by using a self-excited single-phase inverter, one including a self-excited single-phase inverter circuit as shown in FIG. 8 has been used. It was As shown in FIG. 8, the conventional power conversion circuit 80 in the conventional grid-connected power conversion device includes:
Self-excited single-phase inverters U11 to U that use the smoothing capacitor C as a DC voltage source and convert the DC voltage source into an AC output.
13 and U21 to U23, each of which is connected in parallel so that the DC circuit parts of the self-excited single-phase inverter are shared, and their outputs are connected via a multiple transformer Tr to a three-phase AC power system. It is connected to each phase of Vs. This conventional power conversion circuit 80 is
Since each inverter is operated so as to supply only reactive power, a separate DC voltage source is not required and only the smoothing capacitor C is required.

In addition, the conventional system interconnection power conversion device has three
Inputting / outputting reactive power with the phase AC power system Vs,
The reactive power is compensated by controlling the output of the conventional power conversion circuit 80 included in the converter. At this time, the self-excited single-phase inverters U11 to U13 and U21
The power loss due to the device loss in U23 is supplied from the three-phase AC power system Vs.

Explaining the specific operation, the conventional system interconnection power conversion device includes self-excited single-phase inverters U11 to U13 and U2 in the conventional power conversion circuit 80 of the device.
A switching pulse signal from a switching pulse generator (not shown) is input to 1 to U23, and the switching pulse switches ON / OFF of a switching element forming an inverter to convert a DC input into an AC output. There is. These switching elements do not require a forced commutation circuit, such as power transistors, GTO (Gate Turn Off) thyristors, and IGBT (I
A self-extinguishing element such as a nsulated gate bipolar transistor is used.

That is, each self-excited single-phase inverter U11-U11
As shown in FIG. 8, U13 and U21 to U23 are provided with first to fourth switching element sections 81 to 84 in which switching elements and diodes are connected in parallel in mutually opposite directions. A pulse signal is supplied, and one of the combination of the first switching element section 81 and the fourth switching element section 84 and the combination of the second switching element section 82 and the third switching element section 83 are in the ON state. In this case, the other DC voltage is converted into an AC voltage by switching the other so that it is turned off. Each self-excited single-phase inverter U11 to U13
When the output voltage of the smoothing capacitors U21 to U23 decreases due to the device loss, the power equivalent to the device loss is supplied from the three-phase power system, the smoothing capacitor is charged, and the loss is corrected.

Furthermore, the output of each self-excited single-phase inverter is
In the multiple transformer Tr, a self-excited single-phase inverter U1
The outputs of 1 and U21 are serially multiplexed and input to one phase of the three-phase AC power system Vs. Similarly, the outputs of the self-excited single-phase inverters U12 and U22 and the outputs of U13 and U23 are serially multiplexed and input to the corresponding phases.

[0007]

However, in the conventional system interconnection power conversion device, since the direct current circuit is common, the multiple transformer for combining the outputs of the serially multiplexed inverters is used as the device and the power converter. It was necessary to connect with the system, and there was a tendency for the device to become larger and more expensive.

Therefore, the present invention has been made by paying attention to the unsolved problem of the conventional technique as described above, and a plurality of self-excited single-phase inverters are directly connected to each other while keeping their DC circuits independent. An object of the present invention is to provide a system interconnection power conversion device having a configuration in which outputs are multiplexed by connecting in series and the outputs are connected to an AC power system via a reactor, and a multiple transformer is not required for series multiplexing.

[0009]

In order to achieve the above object, a grid interconnection power converter according to a first aspect of the present invention includes a smoothing capacitor as a DC voltage source, and the DC voltage is converted into an AC voltage. A plurality of self-excited single-phase inverters for conversion and a reactor that suppresses changes in output current of the plurality of self-excited single-phase inverters are provided, and reactive power is generated by inputting and outputting electric power to and from an AC power system. A system interconnection power conversion device for compensating the above, comprising at least one self-excited single-phase inverter connected in series with their respective DC circuit parts being independent, and the overall output thereof. Is configured to be connected to the AC power system via the predetermined reactor, and device loss detection means for detecting device loss of each of the plurality of self-excited single-phase inverters, and Output voltage control means for independently controlling the output voltages of the plurality of self-excited single-phase inverters so that the voltage of each smoothing capacitor in the plurality of self-excited single-phase inverters becomes a desired voltage based on the output result. , Is provided.

With such a configuration, a plurality of self-excited single-phase inverters are connected in series and the outputs thereof are multiplexed while the DC circuit portion such as the smoothing capacitor forming the self-excited single-phase inverter is independent. Therefore, the multiplexed output is connected to a predetermined AC power system, and the connection to the power system only needs to be connected via a reactor that suppresses changes in the output current of the self-excited single-phase inverter. Since a large device such as a multiple transformer for multiplexing the outputs is not required, the device can be downsized and the cost can be reduced.

Further, the device loss detecting means detects each device loss of the self-excited single-phase inverter, and the output voltage control means independently controls each output voltage of the self-excited single-phase inverter based on the detection result. Then, adjust the output voltage of each inverter so that even if the output current of each inverter is the same so that the DC voltage of the smoothing capacitor becomes the desired voltage, active power that corrects each device loss is drawn from the power system. To do. That is, when the voltage of the smoothing capacitor of the self-excited single-phase inverter drops due to device loss, the output voltage control means controls the output voltage of the self-excited single-phase inverter connected in series, thereby smoothing the smoothing capacitor in the same inverter. Is controlled to a desired voltage to compensate the reactive power.

[0012] According to a second aspect of the present invention, there is provided a grid interconnection power converter including a plurality of self-excited single-phase inverters each including a smoothing capacitor as a DC voltage source and converting the DC voltage into an AC voltage. It is a grid-connected power converter that includes a reactor that suppresses changes in the output current of a plurality of self-excited single-phase inverters and that compensates reactive power by inputting and outputting power to and from an AC power system. And two or more self-excited single-phase inverters, each of which has a direct current circuit portion connected in series as it is, and the total output thereof is the predetermined reactor via the predetermined reactor. Device loss detection means for detecting the device loss of each of the plurality of self-excited single-phase inverters connected to an AC power system, and the plurality of self-excited devices based on the detection result. Switching frequency control means for independently controlling the frequency of the switching signal supplied to each of the switching elements forming the plurality of self-excited single-phase inverters so that the respective device losses in the single-phase inverter become desired losses. And are provided.

With such a configuration, a plurality of self-excited single-phase inverters are connected in series and the outputs thereof are multiplexed while the DC circuit portion such as the smoothing capacitor constituting the self-excited single-phase inverter is kept independent. Therefore, the multiplexed output is connected to a predetermined AC power system, and the connection to the power system only needs to be connected via a reactor that suppresses changes in the output current of the self-excited single-phase inverter. Since a large device such as a multiple transformer for multiplexing the outputs is not required, this leads to downsizing and cost reduction of the device.

Further, the device loss detection means detects each device loss of the self-excited single-phase inverter, and the switching frequency control means determines the switching frequency of the switching signal supplied to the self-excited single-phase inverter based on the detection result. By controlling so that the device loss of each self-excited single-phase inverter will be the desired loss, the device loss will be reduced even if the output current and output voltage of each inverter connected in series are the same. By directly controlling, the DC voltage of the smoothing capacitor can be controlled to a desired voltage. That is, when the device losses of the self-excited single-phase inverters connected in series are different, the switching frequency control means controls the switching frequency of the switching signal supplied to the self-excited single-phase inverters, so that the self-excited single-phase inverters are controlled. The reactive power can be compensated by controlling the device loss generated in the phase inverter and controlling the DC voltage of the smoothing capacitor of the inverter to a desired value.

According to a third aspect of the present invention, there is provided a system interconnection power converter including a plurality of self-excited single-phase inverters which include a smoothing capacitor as a DC voltage source and convert the DC voltage into an AC voltage. And a reactor that suppresses a change in output current of a plurality of self-excited single-phase inverters, and a system interconnection power conversion device that compensates reactive power by inputting and outputting electric power with a three-phase AC power system. In addition, two or more self-excited single-phase inverters, each of which has a direct current circuit portion connected in series as it is, are provided with three, and the entire output is the predetermined reactor through the predetermined reactor. Device loss detection means for detecting the device loss of each of the plurality of self-excited single-phase inverters, which is connected to each phase of the three-phase AC power system, and based on the detection result. The output voltage control means for independently controlling the output voltage of each of the plurality of self-excited single-phase inverters so that the voltage of each smoothing capacitor in each of the plurality of self-excited single-phase inverters becomes a desired voltage. Is characterized by.

With such a configuration, a plurality of self-excited single-phase inverters are connected in series and the outputs thereof are multiplexed while the DC circuit portion such as the smoothing capacitor constituting the self-excited single-phase inverter is kept independent. Since three are connected in parallel, the output of each multiplexed self-excited single-phase inverter will be connected to each phase of the three-phase AC power system,
For connection to each phase, it suffices to use a reactor that suppresses changes in the output current of each of the multiplexed self-excited single-phase inverters, and a large transformer such as a multiple transformer that combines the outputs of the multiplexed inverters. Since no device is required, this leads to downsizing and cost reduction of the device.

The device loss detection means detects the device loss of each of the self-excited single-phase inverters connected in series, and the output voltage control means detects the output voltage of each self-excited single-phase inverter based on the detection result. The output of each inverter is controlled so that the DC voltage of the smoothing capacitor becomes a desired voltage, and even if the output current of each inverter is the same, active power that corrects each device loss is drawn from the power system. Adjust the voltage. That is, when the DC voltage from the smoothing capacitor of the self-excited single-phase inverter decreases due to the device loss, the output voltage control means controls the output voltage of the self-excited single-phase inverter connected in series, thereby The DC voltage of the smoothing capacitor is controlled to a desired voltage to compensate the reactive power.

According to a fourth aspect of the present invention, there is provided a grid interconnection power converter including a plurality of self-excited single-phase inverters each including a smoothing capacitor as a DC voltage source for converting the DC voltage into an AC voltage. And a reactor that suppresses a change in output current of a plurality of self-excited single-phase inverters, and a system interconnection power conversion device that compensates reactive power by inputting and outputting electric power with a three-phase AC power system. In addition, two or more self-excited single-phase inverters, each of which has a direct current circuit portion connected in series as it is, are provided with three, and the entire output is the predetermined reactor through the predetermined reactor. Device loss detection means for detecting the device loss of each of the plurality of self-excited single-phase inverters, which is connected to each phase of the three-phase AC power system, and based on the detection result. The frequency of the switching signal supplied to each of the switching elements constituting the plurality of self-excited single-phase inverters is independently controlled so that the device loss in each of the plurality of self-excited single-phase inverters becomes a desired loss. And a switching frequency control means for controlling the switching frequency.

With such a configuration, a plurality of self-excited single-phase inverters, which are serially multiplexed, are connected in parallel while the DC circuit portion such as the smoothing capacitor forming the self-excited single-phase inverter is kept independent. Since they are connected, the output of each multiplexed self-excited single-phase inverter will be connected to each phase of the three-phase AC power system, and the connection to each phase will be the multiplexed self-excited single-phase inverter. It suffices to use a reactor that suppresses changes in the output current of each inverter, and it does not require a large device such as a multiple transformer that synthesizes the outputs of the multiplexed inverters. It will be possible.

Further, the device loss detection means detects each device loss of the self-excited single-phase inverter, and the switching frequency control means determines the switching frequency of the switching signal supplied to the self-excited single-phase inverter based on the detection result. By controlling so that the device loss of each self-excited single-phase inverter will be the desired loss, the device loss will be reduced even if the output current and output voltage of each inverter connected in series are the same. By directly controlling, the DC voltage of the smoothing capacitor can be controlled to a desired voltage. In other words, when the device losses of the self-excited single-phase inverters connected in series are different, the switching frequency control means controls the switching frequency of the switching signal supplied to the self-excited single-phase inverter, whereby By controlling the generated device loss and controlling the DC voltage of the smoothing capacitor of each inverter to a desired value, it becomes possible to compensate the reactive power.

According to a fifth aspect of the present invention, in the grid-connected power conversion device according to any one of the first to fourth aspects, the power loss detecting means detects the DC voltage of the smoothing capacitor. It is characterized in that it detects the difference, calculates the difference between this detection result and a preset reference DC voltage, and outputs the calculation result as the device loss.

That is, the device loss detecting means detects the DC voltage of the smoothing capacitor as the device loss, and calculates and outputs the difference between the detected voltage and the preset reference DC voltage.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 are diagrams showing an embodiment of a grid interconnection power conversion device according to the present invention. First, the configuration of a first system interconnection power conversion device according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing the overall configuration of a first embodiment of a grid interconnection power conversion device according to the present invention, and FIG. 2 is a diagram showing a power conversion circuit in the grid interconnection power conversion device. . The same parts as those of the conventional example shown in FIG. 8 are designated by the same reference numerals.

As shown in FIG. 1, the first grid interconnection power converter 1 has a three-phase AC power grid Vs having an inductive load.
In the power conversion circuit 2, a power conversion circuit 2 for supplying reactive power including advance and delay, a switching pulse supply unit 3 for generating a switching pulse signal and supplying a switching pulse signal to the power conversion circuit 2, A device loss detection unit 4 that detects the DC voltage output of the smoothing capacitor that constitutes the single-phase AC inverter and calculates the device loss based on the voltage, and the output of the single-phase AC inverter in the power conversion circuit 2 based on this calculation result. The output voltage control unit 5 for controlling the voltage is included, and each output of the power conversion circuit 2 is connected to each phase of the three-phase AC power system Vs via reactors L1 to L3 described later. ing.
Here, in the present embodiment, the three-phase AC power system V
The alternating frequency of s is 50 Hz.

The power conversion circuit 2 includes a self-excited single-phase inverter U11 to U13 and U21 to U23, and a reactance L.
1 to L3 are included. The self-excited single-phase inverters U11 to U13 and U21 to U23 are U11
And U21, U12 and U22, and U13 and U23 are connected in series, respectively, and the output of the final stage of each is connected to the three-phase AC power system Vs via reactances L1 to L3.

Further, as shown in FIG. 2, the self-excited single-phase inverter U11 is composed of switching element sections 81 to 84 and a smoothing capacitor C, and the switching element sections 81 and 83 and 82 and 84 are connected in series, respectively. And each of the serially connected units are connected in parallel. Furthermore, each switching element portion has a configuration in which a switching element and a diode are connected in parallel in opposite directions.

The reactances L1 to L3 are for suppressing changes in the output current of the self-excited single-phase AC inverters connected in series. The switching pulse supply unit 3 includes each self-excited single-phase inverter U11 of the power conversion circuit 2.
Up to U13 and U21 to U23, switching pulses for switching the switching elements 81 to 84 at predetermined timings are generated and supplied to each self-excited single-phase inverter.

The device loss detecting section 4 includes the self-excited single-phase inverters U11 to U13 and U21 in the power conversion circuit 2.
~ U23 detects the DC voltage of the smoothing capacitor C, the detected DC voltage and the preset reference voltage Vr
Is calculated and the calculation result is output to the output voltage controller 5 as a device loss. The output voltage controller 5 controls the output voltage of the corresponding self-excited single-phase inverter when the device losses of the self-excited single-phase inverters connected in series are different based on the input device loss. ,
Based on the device loss, the output voltage of the self-excited single-phase inverter is controlled so that the current DC voltage of the smoothing capacitor C approaches the desired voltage. In this embodiment, control is performed so that the DC voltage of the smoothing capacitor C in each self-excited single-phase inverter connected in series is the same.

A specific operation of the first grid interconnection power converter 1 will be described with reference to FIG. FIG. 3 is a diagram showing an example of the relationship between the device loss and the DC voltage of the self-excited single-phase inverters U11 and U21. The power conversion circuit 2 operates and, as shown in FIG. 3, self-excited single-phase inverters U11 and U2.
Loss of 1 PU11 and PU21, PU21 is PU
When it becomes larger than 11, DC voltage VU11 and VU of self-excited single-phase inverters U11 and U21
As for U21, as shown in the figure, VU11 has a higher voltage than VU21. This is a self-excited single-phase inverter U1.
This is caused by the difference in the device loss between 1 and U21. In such a state, the three-phase AC power system Vs
There is a possibility that the reactive power supplied to the power supply will change and the reactive power compensation performance will deteriorate. Therefore, the first grid interconnection power conversion device 1 calculates the difference between the device losses and controls the output voltage of the self-excited single-phase inverter based on the calculation result to correct the DC voltage of the smoothing capacitor of the inverter. By doing so, the reactive power is stably supplied to the three-phase AC power system Vs.

That is, the first grid interconnection power converter 1
Always detects the device loss of each single-phase inverter by the device loss detection unit 4. That is, the device loss detection processing of the self-excited single-phase inverters U11 and U21 will be described. The device loss detection unit 4 first detects the DC voltage of the smoothing capacitor C of each of the self-excited single-phase inverters U11 and U21. Next, the difference between the detected voltage and the preset reference voltage Vr is calculated, and the calculation result is output as a device loss.

Furthermore, the result of this calculation is the output voltage control unit 5.
To the self-excited single-phase inverters U11 and U
A comparison process (for example, size comparison) of both device losses of 21 is performed. By this comparison process, when the device loss of U21 is larger than the device loss of U11 as described above, the output voltage control unit 5 sets the output voltage of the self-excited single-phase inverter U21 so that the device loss compensation power becomes large. To control.
As a result, the output voltage of the self-excited single-phase inverter U11 and U
A difference occurs between the output voltage of 21 and the three-phase AC power system Vs.
A large amount of active power flowing from the self-excited single-phase inverter U21 flows into the self-excitation single-phase inverter U21. As a result, the DC voltage of the smoothing capacitor C in the self-excited single-phase inverter U21 rises, the device loss is corrected, and the voltage approaches the same value as the DC voltage of the U11. Here, the output voltage control unit 5 controls the output voltage of the self-excited single-phase inverter so that the DC voltages of the smoothing capacitors C of the self-excited single-phase inverters connected in series have the same magnitude. Is supposed to do. In addition, in the said 1st Embodiment, although the series connection part of self-exciting single-phase inverter U11 and U21 was demonstrated, the same may be said of the series connection part of self-exciting single-phase inverter U12 and U22, U13 and U23. Processing is performed.

As described above, according to the first embodiment, the outputs are multiplexed by connecting the self-excited single-phase inverters in series with their DC circuits kept independent, so that when connecting to the power system. However, a large and expensive device that multiplexes outputs such as a multiple transformer is unnecessary, and it is possible to reduce the size and cost of the entire device.

Further, since the DC voltage of the smoothing capacitor C included in the inverter can be controlled by controlling the output voltage of the self-excited single-phase inverter, the output voltage of each self-excited single-phase inverter connected in series can be controlled. Is the same, and even if each device loss is different, it is possible to correct the loss. Further, a second embodiment of the present invention will be described based on FIGS. 4 to 7. First, the configuration of the second system interconnection power conversion device according to the present invention will be described with reference to FIG. FIG. 5: is a figure which shows the structure of a 2nd grid interconnection power converter device.

As shown in FIG. 5, the second system interconnection power conversion device 6 includes a power conversion circuit 2, a device loss detection section 4, and
And a switching pulse control unit 7,
It is connected to the phase AC power system Vs via reactances L1 to L3. Power conversion circuit 2 and device loss detection unit 4
Is the same as the above-mentioned first grid-connected power conversion device 1, and a description thereof will be omitted.

The switching pulse controller 7 controls the switching frequency of the switching pulse signal supplied to the corresponding self-excited single-phase inverter in the power conversion circuit 2 based on the device loss calculated by the device loss detector 4. This is to adjust the device loss of the inverter. That is, the switching frequency of the switching pulse signal supplied to the corresponding self-excited single-phase inverter is controlled so that the DC voltage of the smoothing capacitor C in the corresponding self-excited single-phase inverter approaches the desired voltage. In this embodiment, control is performed so that the DC voltage of the smoothing capacitor C in each self-excited single-phase inverter connected in series is the same.

The specific operation of the second grid-connected power converter 6 will be described with reference to FIGS. 4, 6 and 7. Figure 4 (a)
4 is a diagram showing an example of a device loss relationship when the switching frequencies of the switching pulse signals supplied to the self-excited single-phase inverters U11 and U21 are the same, and FIG.
(B) is a self-excited single-phase inverter U when the switching frequency of the switching pulse signal supplied to the self-excited single-phase inverter U21 is reduced in the state of (a).
It is a figure which shows the relationship of the apparatus loss of 11 and U21.

Further, FIG. 6 is a diagram showing an output voltage waveform of the self-excited single-phase inverter when the switching frequency is lowered when the generated loss is large, and FIG. 7 shows a high switching frequency when the generated loss is small. It is a figure which shows the output voltage waveform of the self-excited single-phase inverter in the case of doing. When the power conversion circuit 2 operates and the switching frequencies of the switching pulse signals supplied to the self-excited single-phase inverters U11 and U21 are the same as shown in FIG. 4, the loss PU11 of the self-excited single-phase inverters U11 and U21 and PU2
1, when PU21 becomes larger than PU11, self-excited single-phase inverters U11 and U21
DC voltage VU11 and VU21 of VU11 is VU2
The voltage is higher than 1. This is a self-excited single-phase inverter U11 similar to the first grid-connected power converter 1 described above.
Is caused by a difference in device loss between U21 and U21. In such a state, the reactive power supplied to the three-phase AC power system Vs changes, and the reactive power compensation performance may deteriorate. There is. Therefore, in the present embodiment, the difference in the device loss is calculated, and the switching frequency of the switching pulse signal supplied to the self-excited single-phase inverter is controlled based on the calculation result to control the loss generated in the inverter. By doing so, the DC voltage of the smoothing capacitor C is corrected and stable reactive power is supplied to the three-phase AC power system Vs.

That is, the second grid interconnection power converter 6
Since the device loss detection unit 4 always detects the device loss of each single-phase inverter, the calculation result is input to the switching pulse control unit 7. Here, the processing of the device loss detection unit 4 is the same as that of the first embodiment, and therefore the description thereof is omitted. Then, the switching pulse control unit 7 first sets the self-excited single-phase inverters U11 and U21.
A comparison process (for example, size comparison) of both device losses is performed.
By this comparison process, when the device loss of the self-excited single-phase inverter U21 is larger than the device loss of U11 as described above, as shown in FIG.
Control is performed so that the switching frequency of the switching pulse signal supplied to the inverter 21 is lowered to reduce the device loss generated in the inverter U21. That is, in order to reduce the device loss of the self-excited single-phase inverter U21,
It suffices to reduce the device loss itself generated by the operation of the inverter. The higher the switching frequency of the switching element, the higher the generated loss. Therefore, the switching pulse control unit 7 controls the switching pulse signal supplied to the self-excited single-phase inverter U21. The control is performed so that the switching frequency is reduced to reduce the generated loss. This allows
Smoothing capacitor C in self-excited single-phase inverter U21
DC voltage rises, and the device loss becomes smaller.
It approaches the same magnitude as the loss of 1. Here, the switching pulse control unit 7 supplies the switching pulse supplied to the self-excited single-phase inverters so that the DC voltages of the smoothing capacitors C of the self-excited single-phase inverters connected in series have the same magnitude. The switching frequency of the signal is controlled.

In order to stabilize the power loss of the entire system of the three-phase AC power system Vs, it is sufficient to stabilize the reactive power. Therefore, as shown in FIG. 4, the self-excited single-phase inverter U is used.
11 and U21 have the same switching frequency, the loss PU11 and PU21 of the self-excited single-phase inverters U11 and U21 are P
When U21 is larger than PU11, as shown in FIG. 7, the switching frequency of the switching pulse signal supplied to the self-excited single-phase inverter U11 having a small loss is increased to increase the inverter U11. Alternatively, the DC voltage of the smoothing capacitor C may be reduced so as to be equal to the DC voltage of the smoothing capacitor C in the self-excited single-phase inverter U21. In addition, in the said 2nd Embodiment, although only the serial connection part of self-exciting single-phase inverter U11 and U21 was demonstrated, self-exciting single-phase inverter U12, U22, U.
Similar processing is performed in the serial connection portion of 13 and U23.

As described above, according to the second embodiment, the outputs are multiplexed by connecting the self-exciting single-phase inverters in series with their DC circuits independent, so that when connecting to the power system. However, a large and expensive device that multiplexes outputs such as a multiple transformer is unnecessary, and it is possible to reduce the size and cost of the entire device.

Further, by controlling the switching frequency of the switching pulse signal supplied to the self-excited single-phase inverter, the loss generated in the inverter is adjusted, and thereby the DC voltage of the smoothing capacitor C is controlled. Therefore, even if the output currents and output voltages of the self-excited single-phase inverters connected in series are the same and the device loss is different, the loss can be corrected.

Here, the output voltage controller 5 shown in FIG.
Corresponds to the output voltage control means according to claims 1 and 3, and the device loss control section 4 shown in FIGS. 1 and 2 corresponds to the device loss detection means according to claims 1 to 5. The switching pulse control section 7 shown in FIG. 2 corresponds to the switching frequency control means described in claims 2 and 4.

In the above embodiment, the DC voltage of the smoothing capacitor that constitutes the self-excited single-phase inverter is detected, and the difference between this voltage and the reference voltage Vr is used as the device loss, but the invention is not limited to this. Any type may be used as long as it indicates the generated loss, such as the difference between the actual reactive power and the reference reactive power. Further, in the above embodiment, the case where two self-excited single-phase inverters are connected in series has been described, but the present invention is not limited to this, and a circuit is configured by connecting two or more self-excited single-phase inverters in series. It may be done.

[0044]

As described above, according to the system interconnection power converter of the present invention, a plurality of self-exciting type power converters are used while the DC circuit parts such as the smoothing capacitors forming the self-exciting single-phase inverter are kept independent. Since the single-phase inverters are connected in series and their outputs are multiplexed, the multiplexed output must be connected to the specified AC power system, and the output current of the self-excited single-phase inverter must be connected to the power system. Since only a reactor for suppressing the change is required and a large device such as a multiple transformer for multiplexing the output of the inverter is not required, the device can be downsized and the cost can be reduced.

Further, the device loss detection means detects each device loss of the self-excited single-phase inverter, and the output voltage control means independently controls each output voltage of the self-excited single-phase inverter based on the detection result. Since the DC voltage of the smoothing capacitor is controlled to be a desired voltage, each inverter is drawn so that active power for compensating for device loss is drawn from the power system even if the output current of each inverter is the same. A desired DC voltage can be controlled by adjusting the output voltage of.

Further, the device loss detecting means detects each device loss of the self-excited single-phase inverter, and the switching frequency control means determines the switching frequency of the switching signal supplied to the self-excited single-phase inverter based on the detection result. By controlling so that the device loss of each self-excited single-phase inverter will be the desired loss, the device loss will be reduced even if the output current and output voltage of each inverter connected in series are the same. By directly controlling, the DC voltage of the smoothing capacitor can be controlled to a desired voltage.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a first embodiment of a grid interconnection power conversion device according to the present invention.

FIG. 2 is a diagram showing an inverter circuit in a system interconnection power conversion device.

FIG. 3 is a diagram showing an example of a relationship between device loss and DC voltage of self-excited single-phase inverters U11 and U21.

FIG. 4A is a self-excited single-phase inverter U11 and U.
21 is a diagram showing an example of a device loss relationship in the case where the switching frequency of the switching pulse signal supplied to 21 is the same, and (b) is a switching pulse supplied to the self-excited single-phase inverter U21 in the state of (a). It is a figure which shows the relationship of the apparatus loss of the self-excited single-phase inverter U11 and U21 when the switching frequency of a signal is reduced.

FIG. 5 is a diagram showing a configuration of a second grid interconnection power conversion device.

FIG. 6 is a diagram showing an output voltage waveform of a self-excited single-phase inverter when the switching frequency is lowered when the generated loss is large.

FIG. 7 is a diagram showing an output voltage waveform of a self-excited single-phase inverter when the switching frequency is increased when the generated loss is small.

FIG. 8 is a diagram showing a conventional power conversion circuit in a conventional grid-connected power conversion device.

[Explanation of symbols]

1 First grid interconnection power converter 2 Power conversion circuit 3 Switching pulse supply unit 4 Device loss detector 5 Output voltage controller 6 Second grid-connected power converter 7 Switching pulse controller 80 Conventional Power Converter Circuit 81-84 1st-4th switching element parts

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoya Eguchi             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 5G066 FA01 FB13 FC01 FC11                 5H007 CA01 CB03 CB05 CC04 CC06                       CC35 DA03 DA06 DC05

Claims (5)

[Claims] 1. A plurality of self-excited single-phase inverters that include a smoothing capacitor as a DC voltage source and convert the DC voltage into an AC voltage, and a reactor that suppresses a change in output current of the plurality of self-excited single-phase inverters. , And a system interconnection power conversion device for compensating reactive power and the like by inputting and outputting electric power to and from an AC power system, wherein two or more self-excited single-phase inverters are provided. One or more direct current circuit parts connected in series as they are independent of each other are provided, and the entire output is adapted to be connected to the alternating current power system via the predetermined reactor. Device loss detection means for detecting each device loss of the single-phase inverter, and the voltage of each smoothing capacitor in the plurality of self-excited single-phase inverters are determined based on the detection result. So that the voltage, the grid interconnection power conversion apparatus characterized by and an output voltage control means for controlling the plurality of the output voltage of self-commutated single-phase inverters independently. 2. A plurality of self-excited single-phase inverters that include a smoothing capacitor as a DC voltage source and convert the DC voltage into an AC voltage, and a reactor that suppresses a change in output current of the plurality of self-excited single-phase inverters. , And a system interconnection power conversion device for compensating reactive power and the like by inputting and outputting electric power to and from an AC power system, wherein two or more self-excited single-phase inverters are provided. One or more direct current circuit parts connected in series as they are independent of each other are provided, and the entire output is connected to the predetermined AC power system via the predetermined reactor. A device loss detecting means for detecting each device loss of the self-excited single-phase inverter, and based on the detection result, each device loss in the plurality of self-excited single-phase inverters is a desired loss. And a switching frequency control means for independently controlling the frequency of a switching signal supplied to each of the switching elements forming the plurality of self-excited single-phase inverters. Power converter. 3. A plurality of self-excited single-phase inverters that include a smoothing capacitor as a DC voltage source and convert the DC voltage into an AC voltage, and a reactor that suppresses a change in output current of the plurality of self-excited single-phase inverters. , A system interconnection power conversion device for compensating reactive power and the like by inputting and outputting electric power to and from a three-phase AC power system, comprising two or more of the self-excited single-phase inverters, Three direct current circuit parts are connected in series as they are independent of each other, and the entire output is connected to each phase of the three-phase alternating current power system via the predetermined reactor. And a device loss detecting means for detecting a device loss of each of the plurality of self-excited single-phase inverters, and smoothing of each of the plurality of self-excited single-phase inverters based on the detection result. As the voltage of the capacitor becomes a desired voltage, the grid interconnection power conversion apparatus characterized by and an output voltage control means for controlling the plurality of the output voltage of self-commutated single-phase inverters independently. 4. A plurality of self-excited single-phase inverters that include a smoothing capacitor as a DC voltage source and convert the DC voltage into an AC voltage, and a reactor that suppresses changes in output current of the plurality of self-excited single-phase inverters. , A system interconnection power conversion device for compensating reactive power and the like by inputting and outputting electric power to and from a three-phase AC power system, comprising two or more of the self-excited single-phase inverters, Three direct current circuit parts are connected in series as they are independent of each other, and the entire output is connected to each phase of the three-phase alternating current power system via the predetermined reactor. And device loss detection means for detecting the device loss of each of the plurality of self-excited single-phase inverters, and each device in the plurality of self-excited single-phase inverters based on the detection result. Switching frequency control means for independently controlling the frequency of the switching signal supplied to each of the switching elements forming the plurality of self-excited single-phase inverters so that the loss becomes a desired loss. And a grid-connected power converter. 5. The power loss detecting means detects the voltage of the smoothing capacitor, calculates a difference between the detection result and a preset reference DC voltage, and outputs the calculation result as the device loss. The grid-connected power conversion device according to any one of claims 1 to 4, wherein: