JPH06311651A - Photovoltaic power generation system - Google Patents

Abstract

PURPOSE:To provide a photovoltaic power generation system excellent in safety and reliability in which high conversion efficiency is exhibited even under partial shade state. CONSTITUTION:A solar cell power generation unit 6 comprises a solar cell string 1 comprising a plurality of solar cell modules connected in series, and a system interconnection inverter 3 for inverting the output from the solar cell string 1. A plurality of solar cell power generation units 6 are connected in parallel with a load 4 and an interconnection protective unit 5 connected with a commercial power system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar power generation system, and more particularly to a solar power generation system including a plurality of solar cell strings and a plurality of power conversion devices.

[0002]

2. Description of the Related Art Solar cells, which have high expectations as clean energy, can extract energy only while the sun is out. For this reason, in order to use the generated power of the solar cell as a stable energy source, the direct current output from the solar cell is converted into alternating current by, for example, an inverter (system interconnection inverter), and the obtained alternating current power is connected to the commercial alternating current system. Therefore, a solar power generation system configured to be used together with a commercial system has been proposed.

FIG. 5 shows a conventional example of a photovoltaic power generation system using this type of grid interconnection inverter. This system is a photovoltaic power generation system of DC200V power generation 3 kW using a grid-connected inverter of PV-WR1800, a product name of SMA, and includes a solar cell array 11, a backflow prevention diode 12, a grid-connected inverter 13, and the like. Composed. The solar cell array 11 has 216 V in series with 7.2 V × 30 sheets, 15 A in 5 A × 3 strings in parallel, and outputs about 3.2 kW. The string (solar cell string) refers to a series body of a plurality of solar cells or solar cell modules.

The backflow prevention diode 12 connected to each solar cell string is for blocking the backflow of current from another solar cell string connected in parallel.
Due to the backflow prevention diode 12, when a partial shade (a hatching portion in FIG. 5) in which a solar cell string is partially shaded occurs or when one of the solar cell strings fails, another solar cell Backflow of current from the strings is prevented, and the solar cell strings can be prevented from failing or igniting. Instead of providing such a backflow prevention diode 12, when one of the solar cell strings has an abnormality or is in a partial shade state, the operation of all the solar cell strings is stopped and other solar cell strings are stopped. There is also a method to prevent backflow from the. However, since it is inefficient to stop the operation of all the solar cell strings due to the abnormality of one solar cell string, the method of installing the backflow prevention diode 12 in each solar cell string is usually adopted.

Further, the grid interconnection inverter 13 is a power conversion device, and the solar cell array 11 is controlled by controlling the maximum output point.
Output to the maximum, convert that power to a desired AC such as 100V, and load 1 such as household electrical appliances.
4 to power. When the capacity of the grid interconnection inverter 13 is smaller than the output of the solar cell array 11, the grid interconnection inverters 13 are connected in parallel as shown in the figure, and one inverter is controlled by the other so-called master. Perform slave operation. In this example, one system interconnection inverter 13 is a low capacity type of 1.8 kW, and two units are connected in parallel to increase the output. The output of the grid interconnection inverter 13 is connected to an external power system such as a commercial power system via a grid protection device 15.

In the conventional solar power generation system having the above configuration, when the power consumed by the load 14 is larger than the power generated by the solar cell array 11, the power shortage from the commercial power system is generated through the interconnection protection device 15. Complemented. When the power generated by the solar cell array 11 is larger than the power consumed by the load 14, surplus power is sold to the commercial power system through the interconnection protection device 15, so-called “reverse power flow” can be performed. .

[0007]

By the way, when installing the solar power generation system as described above in a general household, in a Japanese house adjacent to an adjacent building due to a small site area, a solar cell is installed in a garden. Are difficult to install, so in this type of photovoltaic system the solar cells are usually installed on the roof. When the solar cell is installed on the roof in this way, for example, the solar cell often becomes partially shaded due to the direction of the roof and the shadows of neighboring buildings.

Further, in the solar power generation system, normally, FIG.
Maximum output point control is performed as shown in. However, if the maximum output point control is performed in a state where some of the solar cell strings have the partial shade as described above, an accurate maximum output point cannot be obtained as shown in FIG. 7 depending on the control method. 6 and 7, the solid line represents current and the broken line represents power. Then, as a result of performing the maximum output point control at a place lower than the actual maximum output point, there is a problem that the conversion efficiency in the system deteriorates. In the example of FIG. 7, although the power of 2.5 kW is obtained when the actual maximum output point is tracked and the maximum output point is controlled, only 2.2 kW of power is obtained depending on the control method.

Further, since the conventional photovoltaic power generation system has a structure in which a backflow prevention diode is installed to prevent a backflow in the case where the solar cell string is abnormal or partially shaded as described above, a voltage drop due to the backflow prevention diode is caused. There is also the problem that power loss will occur. For example, in the example of FIG. 5, 0.7V × 5A × 3 = 10.
A power loss of 5 W will occur.

Therefore, an object of the present invention is to operate a Japanese house with a large number of partial shades with a high conversion efficiency, and also with high safety and reliability, it is possible to eliminate the backflow prevention diode in the conventional system. It is to provide a solar power generation system.

[0011]

[Means for Solving the Problems] The above problems are caused by converting a solar cell string formed by connecting a plurality of solar cell modules in series, and converting DC power obtained from the solar cell string into AC power or DC power. The solar power generation system according to the present invention is characterized by comprising a plurality of solar cell power generation units configured with an output power converter.

[0012]

In the solar power generation system of the present invention having the above-described structure, the output of the solar cell string forming each solar cell power generation unit is directly input to the power conversion device, and the external power system is connected via the power conversion device. Are output independently. Since each solar cell power generation unit is independent in this way, even if a partial shade occurs in one solar cell string, the current from the solar cell strings of other solar cell power generation units does not flow backwards. The backflow prevention diode like the above system is unnecessary. Moreover, since the maximum output point control can be performed for each solar cell power generation unit, the system as a whole can be operated with high efficiency.

Further, as described above, each solar cell power generation unit is independent, and the maximum output point control by the power converter can be performed for each solar cell power generation unit, so that the system can be operated with high conversion efficiency. Furthermore, by operating the power converter, the operation of each solar cell string is detected, and if there is an abnormality in some of the solar cell strings, only that solar cell string is disconnected from the system and the system operation is continued. Soft operation becomes possible. Therefore, a very safe and reliable system can be constructed.

[0014]

EXAMPLES Examples of the present invention will be described below. (Embodiment 1) FIG. 1 shows Embodiment 1 of the photovoltaic power generation system according to the present invention.

This solar power generation system includes a solar cell string 1 and a grid-connected inverter (conversion device) 3 for converting the output of the solar cell string 1 into AC power and outputting the AC power. Unit 6
Three of them are connected in parallel to the load 4 and the interconnection protection device 5.

The solar cell string 1 is constructed by connecting 30 solar cell modules in series and combining them at 216V / 5A. The grid-connected inverter 3 is of the 1kW class, and the output of the solar cell string 1 is 100V.
Convert to AC. By connecting three solar battery power generation units 6 in parallel, about 3 kW of power is supplied to the load 4, and is connected to the commercial power system through the connection protection device 5.

In the solar power generation system according to the first embodiment,
For example, when a part of a specific solar cell string 1 has a partial shade as shown by hatching in FIG. 1 and the maximum output point is different for each solar cell string, in the solar cell power generation unit 1 in which the partial shade does not occur, The solar cell power generation unit 1 in which the maximum output point control as shown in FIG. 3 (1.1 kW) and also the partial shade has occurred
Then, the maximum output point control as shown in FIG. 4 (720 kW) is performed. That is, each solar cell power generation unit 1 is controlled according to the conditions. Note that FIG. 4 is an example of a case where a partial shade occurs in 10 solar cell modules among the 30 solar cell modules constituting the solar cell string 1.

By constructing each solar cell string 1 to be directly connected to each system interconnection inverter 3 as in the first embodiment, a backflow prevention diode for preventing backflow from another solar cell string 1 is unnecessary. Becomes As a result, the voltage drop due to the backflow prevention diode is eliminated, and the power loss corresponding to that is eliminated.

In the above example, the system of 3 kW has been described, but the generated power of the system can be easily adjusted only by adjusting the number of solar cell power generation units 1. For example, if the number of units is two, a 2 kW system can be constructed, and if there are five units, a 5 kW system can be constructed.

Further, in this example, the so-called grid interconnection system, which operates in interconnection with the commercial power grid, has been described, but a so-called stand-alone system that only supplies output power to the load may be used. In that case, in this example, the case where the power conversion device is a grid-connected inverter is shown, but a configuration using a DC-DC converter that supplies DC power to the load may be used as the power conversion device. (Embodiment 2) Next, Embodiment 2 of the photovoltaic power generation system according to the present invention is shown in FIG.

In this solar power generation system, the capacities of the respective solar cell power generation units 6 constituting the system are made different from each other. In other words, when actually installing the solar power generation system on the roof of the house, it is rather unusual to be able to install all the solar cell modules of the solar cell strings that make up the system on only one side of the roof,
In most cases, they are grouped and installed separately, such as 45 modules to the south, 30 modules to the west, and 15 modules to the wall.

In this case, in the second embodiment, as in the first embodiment, the solar cell strings 1 are assembled for each group, and these are input to the grid interconnection inverters 3, so that the maximum output points are respectively set. Take control. As a result, the system can be assembled without lowering the conversion efficiency of the system. In the example shown in FIG. 3, a 30-module serial solar cell power generation unit, a 45-module serial power generation unit, and a 15-module serial solar cell power generation unit are combined together. In the example shown in the figure, two 1 kW-class inverters are input in parallel to the central solar cell string 1 composed of 45 battery modules, but a grid-connected inverter 3 having a large capacity is used. If prepared, it is also possible to adopt a mode in which one grid interconnection inverter 3 is used for one solar cell string 1.

Then, by combining the output of each solar cell string 1 and the capacity of each grid interconnection inverter 3 different as in the second embodiment, it becomes easy to construct an optimal system for each home.

[0024]

As described above, in the solar power generation system of the present invention, since each solar cell power generation unit is independent,
Even when a partial shade occurs, there is no backflow from other solar cell power generation units, so the conventional backflow prevention diode can be eliminated. In addition, since maximum output control can be performed for each solar cell power generation unit, it is possible to operate the system as a whole with high efficiency.

Further, in each solar cell power generation unit, the output of the solar cell string is directly connected to the power conversion device, so that only the abnormal solar cell string is disconnected and the fail-soft operation can be continued to continue the system operation. Becomes In addition, it is possible to easily increase or decrease the electric power simply by adding the solar cell power generation unit according to the demand.

In addition, in the present invention, since the system is configured by combining a plurality of solar cell power generation units, the maximum current in each solar cell power generation unit can be suppressed to a low value, and as a result, a cable for extracting a current from the solar cell string is obtained. Has an effect such as a low current consumption, or the size of a power conversion device can be reduced, and has an extremely high industrial utility value.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a solar power generation system according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a solar power generation system according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a maximum output point of a solar cell string in a normal time in the solar power generation system according to the first embodiment.

FIG. 4 is an explanatory diagram of a maximum output point of a solar cell string in a partial shade in the solar power generation system according to the first embodiment.

FIG. 5 is an explanatory diagram of a conventional solar power generation system.

FIG. 6 is an explanatory diagram of a maximum output point of a solar cell array in a conventional solar power generation system during normal operation.

FIG. 7 is an explanatory diagram of a maximum output point at the time of partial shade of the solar cell array in the conventional solar power generation system.

[Explanation of symbols]

 1 solar cell string, 3 grid interconnection inverter, 4 load, 5 grid protection device, 6 PV cell generation unit, 11 PV array, 12 backflow prevention diode, 13 grid interconnection inverter, 14 load, 15 grid protection device .

Claims (5)

[Claims] 1. A solar cell string formed by connecting a plurality of solar cell modules in series, and a power conversion device for converting DC power obtained from the solar cell string into AC power or DC power and outputting the AC power. A solar power generation system comprising a plurality of solar battery power generation units. 2. The solar power generation system according to claim 1, wherein the power conversion devices forming the solar cell power generation unit are connected in parallel to a power system via a load, respectively. 3. The solar power generation system according to claim 1, wherein the power conversion devices that constitute the solar cell power generation unit are connected in parallel and are connected to a power system via a load. 4. The solar power generation system according to claim 1, wherein each of the power conversion devices forming the solar cell power generation unit performs maximum output point control. 5. The solar power generation system according to claim 4, wherein the solar cell power generation units have different power generation capacities.