JPH06197455A - Solar power generating system - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the nighttime power consumption of grid-connected inverters and grid protection devices in grid-connected photovoltaic power generation systems and improve the system's full-day conversion efficiency. [Configuration] The DC output of the solar cell 1 is converted into AC power by the grid interconnection inverter 2, and this AC power flows to the load 3 and the interconnection protection device 4 via the insulation transformer 6 and the switch 81, and is further connected. Connect to the commercial system 5 via the system protection device 4,
The time measuring means 7 is a switch 81 as a power control means for opening and closing the power supplied to the grid interconnection inverter 2 and the insulation transformer 6, and an opening and closing as a power control means for opening and closing the power supply to the interconnection protection device 4. The container 82 is provided. The time measuring means 7 and the switches 81 and 82 reduce or cut off the power flowing from the commercial grid 5 to the grid grid inverter 2 and grid protection device 4 at night when the solar cell 1 does not generate power. As a result, the net AC output power per day of the solar power generation system is increased, and the all-day conversion efficiency is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generation system, and more particularly to a photovoltaic power generation system which is connected to a commercial grid.

[0002]

2. Description of the Related Art In recent years, interest in environment and energy has been rapidly increasing due to global warming and radioactive contamination due to nuclear accident. Under these circumstances, solar cells are expected worldwide as a renewable and inexhaustible clean energy source. However, as a matter of course, the solar cell can extract energy only during the daytime when the sun is out. Therefore, some auxiliary means is required to use the solar cell as a stable energy source.

The best method as such an auxiliary means is
It is a method to use in combination with a commercial system by converting the direct current output obtained from the solar cell into an alternating current by an inverter (system interconnection inverter) and connecting this to the commercial alternating current system that we use everyday. .

This method is considered to be a favorite for the spread of the system using the solar cell because the land for the installation is unnecessary if the solar cell is installed on the roof. In Japan as well, the legal system has recently been improved, and finally, this type of solar power generation system that is connected to a commercial grid has become practically available.

An example of a solar power generation system is shown in FIG.
DC power output from the solar cell array 1 made by combining a plurality of solar cells in series and parallel is converted into AC power via the grid interconnection inverter 2, and this AC output is passed through the insulation transformer 6 to the load 3 Is connected to the system interconnection protection device 4. Further, the commercial system 5 is connected to the load 3 and the system interconnection inverter 2 via the system interconnection device 4. The grid interconnection inverter 2 has functions such as tracking of the maximum output point of the solar cell and power factor 1 control.

In the solar power generation system having the above structure, when the power consumption in the general-purpose load is smaller than the output of the grid interconnection inverter, the surplus power is reversely flowed to the commercial system, and the power consumption in the general-purpose load is reduced. When it is larger than the output of the grid interconnection inverter, the shortage is supplied from the commercial grid. In this way, solar cell power generation equipment can be used as a stable energy source.
As a technical safety equipment standard for this purpose, the Ministry of International Trade and Industry has established a "system interconnection guideline".

Further, according to the above-mentioned "guidelines", it is required to install facilities so that the grid-connected photovoltaic power generation system does not operate independently when the commercial grid is out of power. Therefore, by combining an underpower relay and an undervoltage relay as a protective relay to provide an islanding prevention function, and by supplying the control power for the grid-connected inverter from the commercial grid side, the grid-connected inverter can be operated during a grid power failure. Is configured not to work. In addition, the control device of the grid interconnection inverter and the grid interconnection protection device are turned on as long as the commercial grid does not lose power, and constantly monitor the system.

By the way, one of the indexes showing the performance of the solar power generation system is the all-day conversion efficiency. All-day conversion efficiency is
It is expressed by the following equation.

Full-day conversion efficiency = (generated power-standby power consumption) / total solar radiation (1) This full-day conversion efficiency does not normally include load power consumption,
Only the part that contributes to power generation is considered. Therefore, in order to increase the all-day conversion efficiency, a method of increasing the instantaneous conversion efficiency of the grid interconnection inverter and the conversion efficiency of the solar cell, that is, increasing the generated power of the above formula has been mainly performed.

[0010]

However, since the solar power generation system naturally generates power only in the daytime, no matter how the conversion efficiency is increased, if the power consumption at night is not reduced, the all-day conversion efficiency can be improved. Absent. However, the conventional solar power generation system has not found any means for reducing the power consumption at night.

The present invention has been made in view of the above problems, and reduces night-time power consumption of a control part in a grid-connected photovoltaic power generation system, that is, a grid inverter and a grid protection device, and improves all-day conversion efficiency of the system. The purpose is to let.

[0012]

The above object of the present invention is to provide a solar cell and a grid interconnection inverter that converts direct current generated by the solar cell into alternating current and supplies the alternating current to a commercial system.
Sunlight comprising an interconnection protection device, time measurement means, and power control means for controlling the power flowing from the commercial system to the grid interconnection inverter or the interconnection protection device based on the output of the time measurement means. Completely achieved by the power generation system.

[0013]

In the solar power generation system of the present invention, the time is measured by the time measuring means, and during the predetermined time, more specifically, at night, the power control means is used for the grid-connected inverter or the grid protection device. Reduce or cut off the power flowing from the commercial grid.

Further, even if the electric power of the control system is reduced or cut off, the solar cell generates electric power only in the daytime, so that the operation and safety of the system are not affected at all. Further, since the interruption operation is performed by measuring the time, the operation can be performed extremely stably, and the unstable operation such as chattering does not occur. In this way, the power consumption of the system at night can be reduced and the all-day conversion efficiency can be increased.

[0015]

EXAMPLES The present invention will be described in more detail based on the following examples.

(Embodiment 1) FIG. 1 shows an embodiment of a photovoltaic power generation system according to the present invention.

In this embodiment, USSC is used as the solar cell 1.
A 1.2 KWp array was constructed using UPM880 manufactured by the same company. This solar cell 1 uses amorphous silicon as a photoelectric conversion semiconductor and is characterized by being lighter than a crystalline silicon cell. As a matter of course, in the structure of the present invention, the solar cell using crystalline silicon or compound semiconductor does not pose any problem.

The DC power output from the solar cell 1 is guided to the grid interconnection inverter 2 and converted into AC. As the system interconnection inverter, a 2KVA inverter made by Nippon Batteries was used. The standby power of this inverter was 40W. The converted AC power is supplied to the insulation transformer 6
And through the switch 81 to the load 3 and the interconnection protection device 4, and the commercial protection system 5 through the interconnection protection device 4.
Connected to. As the interconnection protection device 4, a protection relay for grid interconnection made by OMRON was used. The power consumption of the interconnection protection device was 10 W. The loss of the insulation transformer 6 is 1
It was 0W.

The time measuring means 7 has a control output. This control output is a switch 81 as a power control means for opening and closing the power supplied to the grid interconnection inverter 2 and the insulation transformer 6, and a switching control as a power control means for opening and closing the power supply to the interconnection protection device 4. Input to the container 82. The time measuring means 7 is a combination of a real-time clock and a comparison circuit, and is configured, for example, as shown in FIG.
In FIG. 2, the real-time clock 71 outputs time, and the output time and the operation stop time stored in the memory 72a are compared by the comparator 73a. The output of the comparator 73a is input to the reset terminal of the RS flip-flop 74, and the flip-flop 74 is reset. Memory 7
The operation start time is written in 2b, and the comparator 73
The output of flip-flop 74 is set using b.
In this way, the time measuring means 7 is turned off from the operation stop set time to the operation start time, and is turned on from the operation start time to the operation stop time.

In the present invention, the time measuring means is not limited to the one in the above-mentioned embodiment, but may be of any type as long as it can generate two set times and ON / OFF signals corresponding thereto. The intent of the invention can be achieved. However, it is necessary to select one with low power consumption. In many cases, the power consumption of the time measuring means can be designed to be extremely small, and it operates with a very low power consumption of about several tens of mW. In particular, with a real-time clock with a calendar, the operation start and end times can be automatically changed according to the season, so that the effect of the present invention can be further enhanced. That is, since the time of sunrise or sunset changes depending on the season, the stop time and the start time are changed accordingly. The power source of the time measuring means 7 may be supplied from the system side, or may be a battery in some cases. If it is a cylindrical lithium battery,
It can last up to 10 years.

As the switches 81 and 82, mechanical contactors, semiconductor relays, power relays or the like are used. In the case of mechanical contacts, these switches 81, 82 are preferably pulse drive type which is driven by an electric pulse signal. Since the pulse drive type changes the open / close state with one pulse, the overall power consumption can be suppressed. A semiconductor relay called a photomos relay is inexpensive, has low loss and high reliability, and can be directly connected to the time measuring means as described above, and thus is suitable for the present invention. In this example, a photomos relay manufactured by OMRON was used.

The operation of this embodiment having the above configuration will be described below. In this embodiment, the operation stop time is set to 18
If the operation start time is set to 6:00:00 and the operation start time is set to 6:00:00, the comparator 73a will be activated at 18:00:00.
Outputs an ON pulse having a time width of 1 second, whereby the output of the time measuring means 7 is turned OFF and the switch 81
And 82 are opened. At this time, the power supply to the insulation transformer 6, the grid-connected inverter 2, and the grid protection device 4 is cut off, and the power is saved. As a matter of course, since the solar cell output is close to 0 at the above time, it is not necessary to make the grid interconnection inverter or the like stand by. Further, when the time becomes 6:00:00, the output of the time measuring means 7 becomes O.
N, the switches 81 and 82 are closed.

System interconnection inverter 2, interconnection protection device 4
The total standby power consumption of the (protective relay) and the insulation transformer 6 is 60 W.
60 × 12 hours = 720 Wh of electricity can be saved per day. Further, since the amount of power generation per day in the solar power generation system of about 1.2 kWp as in the present embodiment is only about 6 kWh at most on a fine day, the implementation of the present invention can improve the conversion efficiency of 10% or more all day. It can be improved. On a day with a small solar cell output, such as a cloudy day, the amount of power generation becomes smaller, so the improvement effect is even greater.

As a kind of the present invention, the control power source of the grid interconnection inverter is turned ON / O depending on the brightness, for example.
Although a configuration of FF is conceivable, this configuration may cause a malfunction depending on the installation location of the brightness detector, or a chattering operation (rapid repetition of ON / OFF) depending on the threshold of ON / OFF operation. There is. In this respect, in the present invention, since the time measuring means is used, the operation is stable and the unstable operation such as chattering is never caused.

(Embodiment 2) Another embodiment of the present invention is shown in FIG. In this embodiment, the solar cell 1, the insulation transformer 6, and the interconnection protection device 4 have the same configuration as in the first embodiment, but the time measuring means 7 and the power control switch 91 are connected to the interconnection inverter. Example 1 is that it is built in 2
Is different from. The interconnection inverter 2 has a built-in control microcomputer, and the time measurement means 7 is realized by software using this. Switch 91
A keep relay having a metal contact was used as. The keep relay can be driven by electric pulses and also has the function of the flip-flop in the first embodiment. Further, as a matter of course, since it has a metal contact, it has a feature that the resistance at the time of ON is small and the loss is very small. With this configuration, the loss of the interconnection protection device 4 and the insulation transformer 6 cannot be saved, but since it can be operated only by the grid interconnection inverter 2, the interconnection protection device and the insulation transformer protect the grid interconnection inverter. It is very effective when it can be composed of only functions.

(Embodiment 3) Still another embodiment of the present invention is shown in FIG. The present embodiment is characterized in that, in the configuration of the second embodiment, the switch 91 is not used as the power control means, but the clock signal switching means 101 to the control circuit is used. For the clock signal opening / closing means 101, a tristate TTL gate or the like is usually used. This configuration requires that the control system is a digital control system and operates statically, and can be used only in such a configuration. Further, in this configuration, since the opening / closing means for the power line is unnecessary, it can be mounted on a control microprocessor board or integrated into an IC, for example.

[0027]

As described above, according to the present invention, the solar cell, the grid interconnection inverter for converting the direct current generated by the solar cell into the alternating current and supplying it to the commercial grid, the interconnection protection device,
A solar power generation system having time measuring means and power control means for controlling the power flowing from the commercial grid to the grid interconnection inverter or interconnection protection device based on the output of the time measurement means. Have an effect,
Very high industrial utility value.

(1) It is possible to minimize the power to the grid-connected inverter or grid protection device at night when the solar cell does not generate power. Therefore, the net AC output power per day of the solar power generation system is increased, and the all-day efficiency is improved. The effect is particularly high on small-scale systems such as private houses and on cloudy days.

(2) There is no influence on the safety or operation of the system, and no burden or danger is given to the user.

(3) Since the time measuring means, the power control means and the like are relatively inexpensive, the system cost is slightly increased and the power saving effect is extremely large.

(4) Since the breaking operation is performed by measuring the time, the operation is extremely stable and the unstable operation such as chattering is never caused.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of a configuration example of time measuring means in the embodiment of FIG.

FIG. 3 is an explanatory diagram of another embodiment of the solar power generation system according to the present invention.

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

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

[Explanation of symbols]

 1 solar cell 2 inverter for interconnection 3 load 4 interconnection protection device 5 commercial system 6 insulation transformer 7 time measuring means 81, 82, 91 switch 101 101 clock signal switching means

Claims (3)

[Claims] 1. A solar cell, a grid interconnection inverter that converts direct current generated by the solar cell into alternating current and supplies the alternating current to a commercial system, an interconnection protection device, a time measuring means, and an output of the time measuring means. A photovoltaic power generation system comprising power control means for controlling the power flowing from the commercial grid to the grid-connected inverter or the grid protection device based on the above. 2. The solar power generation system according to claim 1, wherein the power control means is a mechanical opening / closing means driven by an electric pulse signal. 3. The solar power generation system according to claim 1, wherein the power control means is a clock signal opening / closing means for a control circuit.