JP5695820B2 - Inverter - Google Patents

Description

The present invention relates to a power conditioner.

  In recent years, the spread of solar power generation systems has been increasing against the background of increasing awareness of environmental conservation, such as international efforts to reduce CO2 to prevent global warming. In this solar power generation system, solar light energy is converted into direct current by a solar cell module, and this direct current is converted into alternating current power so that it can be used in the home by a power conditioner. Specifically, the power conditioner includes an inverter that receives the output of the solar cell and converts it into a predetermined alternating current, converts the output of the inverter into an appropriate voltage via a transformer, and supplies power to the load. Is done.

  There exists a thing of patent document 1 as a well-known example about the efficiency of this power conditioner. The power conditioner disclosed in Patent Document 1 discloses MPPT (Maximum Power Point Tracking) control for efficiently extracting electric power from a solar cell.

JP2008-300745

The power conditioner described in Patent Document 1 is not intended to achieve high efficiency by paying attention to the output in solar power generation under natural conditions, and further improvement in efficiency is desired. Here, the amount of power generation varies depending on the conditions of solar radiation hitting the solar cell module and the temperature of the module. For example, the output is rated under the conditions of AM 1.5, irradiance 1000 W / m 2, and module temperature 25 ° C.
However, it is rare that the rated output is output under natural conditions, and the inventors calculated the cumulative value of the annual power generation by experiment and calculated the conversion efficiency (partial load efficiency) in the output band below the rated output. I found it necessary to increase. Patent Document 1 does not consider this point, and it is desirable to realize a more efficient solar power generation system from this point.

In addition, the power conditioner may be configured by placing a transformer, an inverter, or the like in the same casing, but it is desirable that the power conditioner be downsized. However, the above-mentioned patent document 1 does not disclose anything about the configuration considering this miniaturization.
In view of the above problems, a first object of the present invention is to provide a power conditioner capable of improving partial load efficiency and improving system conversion efficiency in a photovoltaic power generation system in a power conditioner equipped with a transformer. To do.
A second object of the present invention is to provide a power conditioner that can be further reduced in size in a power conditioner configured by putting a transformer and an inverter in the same casing.

In order to solve the above problems, in one embodiment of the present invention, a power conversion device that converts direct current power from a solar cell to generate alternating current power is provided, and the power of the solar cell is linked to a commercial power system power supply. In the power conditioner, an amorphous transformer that boosts the power generated by the power conversion circuit is provided between the power conversion circuit and the commercial power system.
Further, in the above aspect, more desirable embodiments are as follows.
(1) A current transformer that detects the output current of the inverter, an offset detection means that detects an offset from the detected value of the current transformer, and an offset before the start of operation is detected by the offset detection means, and the offset becomes zero. Offset correction means for performing correction as described above.
(2) The amorphous transformer shall be a dry type transformer.
(3) The offset correction means detects the offset from the detected value of the current transformer before the start of operation, and starts the operation after correcting so that the offset becomes zero.
(4) The power converter and the amorphous transformer are housed in one housing, and a partition is provided between the power converter and the amorphous transformer.
(5) The output voltage of the amorphous transformer is 1 kV or less.
(6) Provided with a first blower that blows air to the power converter and a second blower that blows air to the amorphous transformer.
(7) The cooling capacity of the first blowing means is larger than the cooling capacity of the second blowing means.

  According to one embodiment of the present invention, an efficient power conditioner can be provided. In addition, according to another embodiment of the present invention, it is possible to reduce the size of the inverter while suppressing the amount of heat generated by the power conditioner.

The figure for demonstrating the whole structure of a solar energy power generation system. The figure for demonstrating the circuit diagram of the power conditioner of a present Example. The figure for demonstrating the partial load ratio of a photovoltaic power generation system. The figure for demonstrating the characteristic of the transformer of a silicon steel plate, and an amorphous transformer. The figure for demonstrating the loss by the characteristic of the transformer of a silicon steel plate, and an amorphous transformer. The figure which looked at the inverter from the side. The top view of the inverter.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example 1 of the present invention will be described.
FIG. 1 is a system configuration example of photovoltaic power generation. The DC output power generated by the solar power generation module 1 is once combined into a single connection box 3 via the DC power transmission unit 2 and converted into AC power by the power conditioner 4. It is connected to the commercial system 6 via the AC power transmission unit 5.
FIG. 2 is a drawing for explaining the entire configuration of a power conditioner equipped with a transformer in the present embodiment. The DC power generated by the solar power generation module is converted into AC power by the inverter unit 7. The waveform is converted to a sine wave via the filter unit 8 and boosted to the system voltage by the transformer 9.

Next, the transformer mounted on the power conditioner in the present embodiment will be described. This transformer has a loss in itself, and the greater this loss, the lower the conversion efficiency as a power conditioner, which can hinder high efficiency.
FIG. 3 shows an example of the annual accumulated power generation amount for each output band of the photovoltaic power generation system. FIG. 3 is based on the experiment conducted by the inventor. According to this experiment, in the rated output band of 90 to 100%, only a small amount of power is generated annually, and the power generation is most frequent at 30% to 70%. found. In FIG. 3, the horizontal axis represents the value when the output of the photovoltaic power generation system is rated output = 100%. The vertical axis represents the power generation amount (kWh). In this experiment, the generated power exceeded 12000 kWh in the output band of 30% to 70%. The power generation amount was 2000 kWh at 90% to 100% close to the rated output. In this way, in solar power generation, the amount of power generation in the output band below the rated output is large, so if the load efficiency can be improved especially in this part, it will lead to an increase in the power generation amount of the entire system, resulting in efficiency. A good solar power generation system can be realized.

  Therefore, in this embodiment, an amorphous transformer is adopted. This is because it is possible to improve the above-described partial load efficiency with respect to the silicon steel plate transformer employed in the conventional power conditioner. This point will be described.

  FIG. 4 shows an example of the characteristics of a silicon steel plate transformer and an amorphous transformer. 14 shows the conversion efficiency of the silicon steel plate transformer. In the case of the silicon steel plate transformer, the efficiency in the band with a small load factor is almost the same as that at the rated output. On the other hand, in the case of the amorphous transformer efficiency 13, the conversion efficiency in a band with a small load factor is higher than that at the rated output. The load factor is the ratio of the current output to the rated output. The vertical axis shows the conversion efficiency of the transformer. In FIG. 4, it can be seen that when the load factor is around 40% to 50%, the efficiency of both transformers is reversed at about 98%.

  FIG. 5 shows an example of loss due to characteristics of a silicon steel plate transformer and an amorphous transformer. The horizontal axis shows the load factor. Reference numeral 15 indicates a loss with respect to the load factor of the silicon steel plate transformer, and reference numeral 16 indicates a loss with respect to the load factor of the amorphous transformer. In FIG. 5, it can be seen that the loss of both transformers is reversed at a load factor of 40% to 50%. Moreover, it turns out that the loss in this case is about 500W. As described above, in this embodiment, an amorphous transformer having a load factor of 40% or less and a loss of 500 W or less is adopted. Therefore, the amorphous transformer can reduce loss at a low load factor (low output). Therefore, as described above, in solar power generation, low output power generation increases, so that the loss at this time can be reduced, and as a result, a power conditioner that contributes to an efficient solar power generation system can be realized. .

  Thus, when selecting a transformer as a power conditioner from the difference in efficiency when adopting each transformer of silicon steel plate and amorphous transformer, the partial load efficiency is improved by installing the amorphous transformer. High power conditioner can be provided.

  Here, the DC bias magnetism of the transformer will be described. This DC bias is generated due to the DC component being superimposed on the AC current that passes through the winding of the transformer and becomes the iron core excitation current. The direct current component in the exciting current strengthens the excitation in the superimposing direction, breaks the symmetry in the iron core excitation, and causes the transformer secondary output voltage waveform to be distorted. Therefore, when a transformer is mounted on the power conditioner, it is necessary to suppress the DC bias phenomenon.

  In the case of a transformer made of silicon steel, it is possible to withstand DC bias on the transformer side by performing a process that increases the resistance against DC bias. However, in the case of an amorphous transformer, due to the thickness of the material, it is difficult to process the transformer so that it can withstand a DC bias. In other words, it is necessary to secure an insulation distance in order to withstand the transformer, but in the case of an amorphous transformer, the insulation size is larger than that of a silicon steel plate transformer. This is because the size becomes very large and is not practical.

  Therefore, in this embodiment, the amorphous transformer is not provided with resistance, but the system side is provided with a configuration that suppresses DC bias. This configuration will be described. In FIG. 2, CT detects the output current of the inverter 8 with a current transformer, and PT detects the system voltage with a voltage transformer. Detection values detected in CT and PT are supplied to the control circuit, and the control circuit controls the inverter 7 based on these detection values. When using CT and PT, if the iron core part of the transformer remains magnetized in one biased direction due to an excessive one-way current such as inrush current, the iron core is magnetically saturated as described above. The transformer will not work ideally and the voltage and current cannot be measured correctly.

  Therefore, the power conditioner of the present embodiment has a function of offset correction before starting operation in order to eliminate such DC bias. That is, since the current does not flow through the CT when the apparatus is stopped, the current offset detected at that time is subtracted to correct the current offset to 0 A (ampere). In this case, if an offset more than the specified value occurs, the sensor itself may be broken, and it may not be able to operate normally even if it is operated with offset correction. Therefore, in such a case, a protection function is provided in which an offset error is determined and the operation itself is not performed. Furthermore, during the operation of the device, the DC component is detected by integrating the detected current, and the value obtained by subtracting the DC component target value 0A (ampere) is used as the control command value. Correction control means for reducing the value to 0 is provided.

  As described above, in this embodiment, since the system side is provided with a configuration that suppresses the direct current component, the demagnetization phenomenon can be suppressed and an amorphous transformer can be mounted. Therefore, according to the present embodiment, it is possible to provide a power conditioner that contributes to an efficient photovoltaic power generation system while suppressing the bias magnetism phenomenon of the transformer. Moreover, since direct current bias magnetism is suppressed on the system side, it is not necessary to provide the transformer with an insulation distance, so that the size of the apparatus can be reduced.

  A second embodiment of the present invention will be described. The power transformer of this embodiment is also equipped with an amorphous transformer. As described in Example 1, the amorphous transformer can increase the conversion efficiency particularly when it is used in a power conditioner for photovoltaic power generation, but has a larger physique compared to the conventionally used silicon steel plate transformer. There is a problem that the weight is heavy.

  Therefore, in this embodiment, a dry amorphous transformer is employed to reduce the size of the power conditioner. This dry type transformer is a transformer in which an iron core and a wire are used in the air. On the other hand, a transformer in which the entire surface of the winding is covered with a resin or an insulating base material containing a resin is called a mold transformer. In this embodiment, it is possible to reduce the size of the power conditioner by adopting the above-described dry amorphous transformer.

  However, when a dry-type transformer is employed, the insulation effect is weaker than that of the molded transformer as described above. Therefore, in this embodiment, a power conditioner is used in which the system voltage, that is, the output voltage of the amorphous transformer is 1 kV or less. Since the insulation effect can be reduced by using a low pressure in this way, a dry-type transformer can be employed. And since the insulation distance of a transformer can be shortened, the size of a transformer can be suppressed further and it becomes possible to attain size reduction of a power conditioner as a result. In addition, this insulation distance means the distance between the electroconductive parts in a transformer inside, and the distance of an iron core and an electroconductive part. Although not shown in the figure, an insulation distance must be secured between the iron core and the secondary wire or between the primary wire and the secondary wire inside the transformer. Therefore, the transformer will also become larger.

  In addition, since the transformer and the inverter have heat, this cooling structure is also an important element for the power conditioner. In the case of a mold transformer, the insulation effect is large, while the heat dissipation effect is small and large heat is easily generated. Then, since the inverter cannot withstand the heat of the molded transformer, it may be necessary to use a separate housing from the molded transformer. In this way, even if the problem of heat is solved, there arises a new problem of increasing the size of the apparatus and increasing the cost associated with the increase in size.

On the other hand, the dry amorphous transformer has a small insulation effect, but has a large heat dissipation effect against air. Furthermore, as described above, the size is smaller than that of the molded transformer. Taking advantage of such characteristics, in the present embodiment, both a dry amorphous transformer and an inverter are mounted in one casing.
FIG. 6 is a side view of the power conditioner according to this embodiment. 7 is an inverter, and 9 is an amorphous transformer. Reference numeral 8 denotes a filter unit composed of a reactor. Reference numeral 10 denotes a cooling fan, which is not shown in FIG. 6, but for the purpose of cooling the inverter 7, as described above, in this embodiment, a dry amorphous transformer is used to suppress the amount of heat generation. Each inverter and amorphous transformer can be mounted in a single housing. As a result, the size of the power conditioner can be reduced. Furthermore, even in the same housing, the inverter and amorphous transformer generate different amounts of heat, so it is preferable to have independence, so this is achieved by providing a partition between the inverter and amorphous transformer. To do. Thus, the cooling capacity can be improved by making independent control of the fan that blows air to each of the inverter and the amorphous transformer.

  FIG. 7 shows a view of the inverter from the top. In this manner, the inverter and the amorphous transformer are arranged independently as shown in FIG. 6 and arranged as shown in FIG. 7 so that the cooling fans can be cooled independently. In FIG. 7, 17 is a fan (not shown) for cooling the control panel, and cools the amorphous transformer together with the control panel. Reference numeral 18 denotes a fan for cooling the inverter 7. According to the present embodiment, first, an amorphous transformer is employed to suppress heat generation because the loss is small, and further a heat generation suppression effect is realized by using a dry type transformer. As a result, it was possible to suppress the heat generation of the inverter, and as shown in FIG. 7, the cooling fan for the dry amorphous transformer has a smaller cooling capacity. In FIG. 7, the cooling capacity is changed by changing the number of installed cooling fans. However, the cooling capacity per cooling fan may be changed without changing the number of cooling fans.

  For amorphous transformers with reduced heating power, the size of the cooling fan can be reduced (or the number can be reduced). It can be reduced. When power for driving a cooling fan is supplied from solar power generation or the like, it also has an effect of suppressing a decrease in power generation amount.

  In addition, the cooling fan generally has the longest life factor, but since the heat generation can be reduced, the driving time can be reduced and the life of the cooling fan can be extended. When the cooling fan stops at the end of its life, the power conditioner also stops, so the long life effect of the cooling fan can also improve the reliability of the power generation system.

  Also, the transformer is more resistant to heat than the inverter. Therefore, in this embodiment, the cooling fan 18 for the inverter starts air blowing when the operation of the power conditioner starts, whereas the cooling fan 17 starts operating when the transformer reaches a predetermined temperature or higher. Yes. The inverter has an element that may be broken when it generates heat (for example, IGBT). Therefore, the inverter is always operated, but the temperature of the IGBT is measured, and the cooling fan 18 is operated when the temperature rises above a predetermined temperature. It doesn't matter if you do.

  As described above, the power conditioner used in the solar power generation system has been described in the present embodiment, but the power conditioner may be used in a wind power generation system. If there is much power generation at low output, an improvement in efficiency can be expected as in the case of a solar power generation system.

1 Solar power generation module
2 DC power transmission unit
3 Connection box
4 Power conditioner section
5 AC power transmission section
6 Commercial power system
7 Inverter section
8 Filter section
9 Transformer part
10 Cooling fan section
11 Temperature measurement unit
12 10kW solar power generation system annual cumulative power generation by output band
13 Amorphous transformer conversion efficiency
14 Silicon steel plate transformer conversion efficiency
15 Silicon steel plate transformer loss
16 Amorphous transformer loss
17 Cooling fan for transformer
18 Cooling fan for inverter

Claims (3)

In a power conditioner comprising a power conversion device that converts direct current power from a solar cell to generate alternating current power, and that links the power of the solar cell to a commercial power system power supply,
A dry amorphous transformer whose output voltage for boosting the power generated by the power conversion circuit between the power conversion circuit and the commercial power system is 1 kV or less;
A current transformer for detecting the output current of the inverter;
Offset detecting means for detecting an offset from the detected value of the current transformer;
An offset correction means for detecting a current offset from the detected value of the current transformer before the start of operation by the offset detection means , and subtracting the current offset so that the offset becomes 0 ;
The DC component is detected by integrating the detected current during operation of the inverter, and the DC component is set to 0 by subtracting 0 from the target value of the DC component as the control command value. Correction control means to suppress,
First blowing means for blowing air to the power converter;
Second air blowing means for blowing air to the amorphous transformer ,
The power converter and the amorphous transformer are housed in one housing, and a partition is provided between the power converter and the amorphous transformer ,
The first air blowing means starts air blowing together with the start of operation of the power conditioner, and the second air blowing means starts air blowing when the amorphous transformer reaches a predetermined temperature or more. Power conditioner to do. In the inverter according to claim 1,
The power conditioner is characterized in that the operation is stopped when the offset detected by the offset detection means is a predetermined value or more. The power conditioner according to claim 1,
The power conditioner characterized in that the cooling capacity by the first air blowing means is larger than the cooling capacity by the second air blowing means.

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