JPH06133472A - Sunlight power generating system - Google Patents

Abstract

PURPOSE:To utilize the output of a solar battery effectively by maintaining the voltage at a power receiving terminal normally even if the voltage of an electric power system is high. CONSTITUTION:A solar battery array 1, an inverter 2, which converts the DC generated by the solar battery array 1 into the AC, and an electricity storage means 7 are provided. The output of the inverter 2 is connected to a commercial electric power system 5 through an interconnection protective device 4. When the voltage of the commercial electric power system 5 exceeds a specified value, the generated energy of the solar battery array 1 is stored in a secondary battery 72 constituting the electricity storage means 7.

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 connected to a power system such as a low voltage system used in a general house.

[0002]

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

The best method as such an auxiliary means is
This is a method in which the direct current output from the solar cell is converted into alternating current by an inverter, and this alternating current converted output is connected to a power system such as a commercial alternating current system that we use daily, that is, used together with the power system. This method is considered to be a favorite for the spread of the solar cell system 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 the above-mentioned system interconnection system has become fully practical. An example of this type of system interconnection system is shown in FIG.

In FIG. 10, DC power output from a solar cell array 1 made by combining a plurality of solar cells in series and parallel is converted into AC power via an inverter 2 and then converted to a general load 3. It is connected to the grid interconnection protection device 4. Further, a commercial power system 5 is connected to the load 3 and the inverter 2 via a system interconnection device 4. The inverter 2 receives commands from the control device 6 such as tracking of the maximum output point of the solar cell and control for setting the power factor to 1. In this system interconnection system, when the power consumption of the general-purpose load 3 is smaller than the output of the inverter 2, the surplus is reversely flowed to the commercial power system 5. When the power consumption of the general-purpose load 3 is larger than the output of the inverter 2, the shortage is supplied from the commercial power system 5. By using the grid interconnection system having such a configuration, the solar cell power generation equipment can be used as a stable energy source.

Since an abnormality in the electric power system has a great influence on the whole society, the electric power company strictly maintains and manages the frequency, voltage, harmonic distortion and the like of the commercial electric power system.
For example, in a 100V system used in a general household, the voltage is defined as 101 ± 6V by the Electricity Business Law. As a matter of course, it is necessary to prevent the solar power generation system that flows backward to the grid from deviating from the above voltage range.
In addition to this, the photovoltaic power generation system connected to the electric power system has technical standards such as keeping the power factor close to 1 and suppressing the harmonic current distortion factor to 5% or less. .

[0006]

By the way, in order to connect the commercial power system and the solar power generation system as described above, it is naturally necessary to connect a distribution line between them. Further, since the distribution line has impedance, it is unavoidable that a voltage drop occurs during power transmission.
For example, in the system as shown in FIG. 4, since the distribution line impedance 12 exists between the commercial power system 13 and the customer 11, the power reception voltage VR of the customer 11 is lower than the system voltage VS of the commercial power system 13. I will end up. Therefore, the grid voltage VS of the commercial power grid 13 is equal to the distribution line impedance 1
It is set a little higher in consideration of the voltage drop due to 2. For example, the low-voltage side output of the pole transformer is set to 105V, and when there is no load, the receiving voltage of the customer is 105V.
Becomes Then, when electric power is sent from the solar power generation system to the electric power system, this distribution line impedance causes damage and the voltage at the power receiving end of the customer exceeds 105V. In addition, for example, when 30 A is consumed, the received voltage is 101
If it becomes V, if a reverse flow of 30 A is applied, the amount of voltage drop will be reversed, resulting in 109 V, which exceeds the allowable voltage range.

The simplest method for preventing such inconvenience on the solar power generation system side is to suppress the current generated from the solar cell. However, this method has a problem from the viewpoint of effectively utilizing the energy received from the sun. This is because some of the solar energy will be discarded.

The second method is a phase advancing power injection method proposed by the Central Research Institute of Electric Power Industry. Although this method is effective, since it is necessary to increase the output apparent power, it is necessary to increase the capacity of the inverter, which may adversely affect the overcurrent protection function.
Also, of course, the power factor will be reduced.
That is, according to a calculation by the Central Research Institute of Electric Power Industry, in order to send 3 KW of active power to a standard low voltage system and reduce the voltage to 107 V or less, 3 Kvar of reactive power is required.
The apparent power at this time is 4.2 KVA. Since the output current is 42 A, the overcurrent protection function cannot be activated at least up to this range. Originally 3K
Since the current for W is 30 A, the overcurrent protection function should work at about 33 A, which is an increase of 10%. Further, the power factor at this time decreases to about 0.7.
For this reason, a larger current than the design may flow through the distribution line, which imposes a burden on the distribution line.

There are some that further complicate the voltage maintenance problem. It is the voltage instability of the power system. In order to maintain the voltage for all consumers, the power system responds to changes in demand by opening and closing power stations and substations. For this reason, the voltage of the electric power system is not constant and changes every moment. FIG. 5 shows the measured values of the voltage in the power system on a certain day measured by the present inventor. At the arrow A, the voltage of the system has reached the legal upper limit of 107 V, and it is clear that at this point, when power is sent to the system, the voltage exceeds the upper limit.

As described above, it has been difficult for the existing solar power generation system to effectively use all of the output power of the solar cell while maintaining the voltage at the power receiving end within the legal value.

The present invention has been made in view of the above problems,
An object of the present invention is to provide a solar power generation system that effectively uses the output of a solar cell while maintaining the voltage at the power receiving end at a normal value even when the voltage of the power system is high.

[0012]

According to the present invention, a solar cell, an inverter for converting direct current generated by the solar cell into an alternating current, and a storage means are provided, and the output of the inverter is connected to a power system. In the present photovoltaic power generation system, a photovoltaic power generation system is obtained in which the power generation means stores the power generation energy of the solar cell when the voltage of the power system exceeds a predetermined value.

[0013]

In the photovoltaic power generation system of the present invention, when the output voltage of the inverter, that is, the voltage at the power receiving end reaches the legal upper limit value, electric energy starts to be stored in the storage means. For this reason, the amount of power that flows backward in the power system is reduced, and it is possible to prevent voltage rise. When the voltage of the electric power system drops, the stored electricity is discharged and the stored energy is output to the electric power system. Since it is not necessary to suppress the output of the solar cell during the storage of electricity, solar energy can be effectively used.

Therefore, according to the present invention, solar energy can be effectively utilized while maintaining the legal voltage range. Since a large amount of phase-advancing reactive power does not have to flow into the power system, it does not adversely affect the overcurrent protection function and the like, and does not burden the distribution line.

Since the present invention uses a control system in which electricity is stored in the electricity storage means when the voltage of the power system is high, the secondary battery or the like used in the electricity storage means may have a relatively small capacity, and a large capacity and high cost. You don't have to use anything.

[0016]

EXAMPLES The present invention will be described in detail below based on examples. (Embodiment 1) FIG. 1 shows a photovoltaic power generation system according to Embodiment 1 of the present invention. The DC output generated from the solar cell array (solar cell) 1 is connected to the storage means 7 and the inverter 2. The power storage unit 7 includes a charge / discharge interface 71 and a secondary battery 72. The role of the charge / discharge interface 71 is to match the voltage between the secondary battery 72 and the solar cell array 1, and to control the charge / discharge of the secondary battery. The voltage for extracting the maximum output power from the solar cell is generally determined by the weather conditions at that time. On the other hand, the voltage required to charge the secondary battery 72 is also
It is almost determined by the type of battery, the remaining amount of the battery, the temperature, and the like. Of course, it is necessary to devise the number of series of solar cells and secondary batteries at the time of design so that the difference between these two voltages will be as small as possible, but the voltage change due to weather conditions etc. of the maximum power point of the solar cell It is large and the change in the charging voltage of a secondary battery such as a lead battery is small, whereas matching is difficult to obtain. Therefore, if these batteries are directly connected without voltage matching, the intent of the present invention can be achieved, but there is a slight decrease in efficiency due to voltage mismatch.

The charging / discharging interface 71 is usually
It is composed of a DC / DC converter capable of both voltage step-up and step-down. DC like this
The principle diagram of the / DC converter is shown in FIG. Switch 3
By opening and closing 2, the magnetic energy is stored in the inductance 33 and is supplied to the load as a power source. The output voltage can be controlled by controlling the duty ratio of the switch 32. In the photovoltaic power generation system of the present invention, the controller 6 controls the charging / discharging interface 7
Control 1 Further, as the secondary battery 72, a NiCd battery, a lead battery, a lithium secondary battery, a nickel hydrogen battery or the like can be used.

FIG. 7 shows an example of the inverter 2 used in the first embodiment. The DC power output from the solar cell array 1 is passed through the DC filter 21 to the switching unit 2
2 and is connected to the power system through the AC filter 23. Here, the DC filter 21 is for compensating a sudden change in output due to a sudden change in solar radiation, and an aluminum electrolytic capacitor having a high withstand voltage and a large capacity is used. The switching unit 22 has a function of switching between positive and negative of a DC input and supplying the load to a load, and is a unit responsible for DC-AC conversion. Various methods have been proposed for this DC-AC conversion portion, but the voltage type current control PWM method is mainly used for low voltage system interconnection. This system is characterized in that an output waveform with very little harmonic distortion can be obtained. Also, as the element used for the switching unit,
Power transistor, power MOSFET, IGBT,
There are SIT, thyristor, GTO, etc. Currently, several KW
Power transistor, MOSFE with output capacity
A self-extinguishing type such as a T or IGBT, which can take a high switching frequency, is used.

The output of the inverter 2 is connected to the general load 3 and the interconnection protection device 4, and is connected to the commercial power system 5 via the interconnection protection device 4. Interconnection protection device 4
Has a function of disconnecting the connection between the solar power generation system and the commercial power system 5 in the event of an abnormality such as overcurrent.

The controller 6 controls the charging / discharging interface 71 and the inverter 2.
The control device 6 controls the output voltage and current of the solar cell array 1, the output current and output voltage of the inverter 2, the power factor, and the secondary battery 7.
The entire system is controlled by using the voltage, current, remaining amount, etc. of 2 as input information. Particularly important information in the present invention is
The output voltage of the inverter 2, the output voltage and output current of the solar cell array 1, and the remaining battery level. at least,
Without these four pieces of information, the object of the present invention cannot be achieved. The control device 6 is composed of a microcomputer and its peripheral interface elements. For example, as a microcomputer, Z80, 8086, V30, 6
8000 and the like, and peripheral interfaces include a parallel interface, DMA, A / D converter and the like. Although the control system is configured by the digital control system in the first embodiment, it may be configured by the analog system without any problem. The control means 8 can also control the interconnection protection device 4.

Next, the operation of the first embodiment having the above configuration will be described. When the sun rises and light is incident on the solar cell, an electromotive force is generated in the solar cell array 1. Control device 6
Detects the voltage of the solar cell array 1 and then checks the state of the commercial power system 5. If there is no abnormality in the state of the commercial power system 5, the switching means of the inverter 2 is opened / closed, DC / AC conversion is performed, and energy is discharged to the commercial power system 5. In this state, the duty ratio of the switching means is changed so that the output power of the solar cell array 1 is maximized, and the maximum output is taken out from the solar cell array 1. The phase of the output current at this time is controlled so as to match the output voltage phase, and the power factor is maintained at approximately 1.

At this time, if the output voltage of the inverter 2 is within the legal value, the operation is continued. Inverter 2
If the output voltage of is above the legal value, the controller 6 issues a charge command to the charge / discharge interface 71,
Charging of the secondary battery 72 that has been discharged in advance is started. At this time, the output power of the inverter 2 is lowered while maintaining the maximum output point of the solar cell array 1, that is, the switching means of the inverter 2 and the charging / discharging interface 71 are controlled in synchronization so that the voltage drops to a legal value. Furthermore, in this synchronous control, when the voltage does not drop to the legal voltage, the operation of the inverter 2 is stopped and all the output of the solar cell array 1 is directed to charging. Such a charging operation is continued until the system voltage drops by several V from the legal upper limit value. In the case of a standard low-voltage distribution line, it is desirable to continue the charging operation until the voltage drops by about 3 to 5V, although it depends on the electric power to be used for reverse power flow. Since the voltage of the power system changes every moment and the amount of solar radiation also fluctuates, the high voltage state does not last so long and is within 30 minutes at most. Therefore, a relatively small capacity is sufficient for the secondary battery used in the present invention. For example, a solar battery having a maximum output of 1 KW may have a capacity of 500 Wh. This corresponds to one automobile battery when the depth of discharge is 100%. Naturally, the secondary battery
Since the life is extremely shortened at a discharge depth of 100%, a little more capacity is required, but it is clear that a huge battery is not required. Incidentally, when the fully charged state is reached during the charging operation and the voltage of the system is not lowered, the charging operation is also stopped and the system is in a standby state until the system voltage is lowered.

On the other hand, when the received voltage drops and the output power from the solar cell array 1 becomes sufficiently small, direct current power is sent to the inverter 2 from the secondary battery 72 charged previously through the charge / discharge interface 71. The inverter 2 outputs the output of the solar cell array 1 and the secondary battery 7
The output from 2 is combined and the power is reversely flowed to the commercial power system 5. This operation is continued until the remaining amount of the secondary battery 72 becomes empty. However, if the received voltage exceeds the legal upper limit during operation, the charging operation starts again.

FIG. 8 shows an operation example of the system of the first embodiment. In FIG. 8, the solid line A represents the power reception voltage of the system of the first embodiment. The solid line B represents the power generated by the solar cell array in the system of Example 1, and the horizontal axis represents time. In the system of Example 1, it can be seen that the received voltage is maintained at the legal value and the power factor does not drop, and therefore the output power of the solar cell array is effectively used.

FIG. 9 shows the operation of the conventional system of the type that suppresses the electric power generated from the solar cell (solar cell array). In FIG. 9, when the power receiving voltage shown by the solid line A rises, the output of the solar cell shown by the solid line B is suppressed, so that the output that the solar cell shown by the diagonal line can output is discarded. Recognize. On the other hand, in the system of the first embodiment, energy corresponding to the shaded area in FIG. 9 is stored in the secondary battery. (Embodiment 2) The system configuration of Embodiment 2 of the present invention is shown in FIG. The feature of the second embodiment is that the charging / discharging interface 71 and the secondary battery 72 are arranged on the output side of the inverter 2. In such a configuration, the charge / discharge interface 4 needs to have an inverter function. In this configuration, the power storage unit 7 may have an independent control system separate from the solar cell inverter 2. That is, there is a feature that the system of the present invention can be externally attached to the conventional system. That is, the charging / discharging interface 71 may have the function of monitoring the received voltage and the function of controlling the charging / discharging, and the controller 6 of the inverter 2 may have the maximum power point tracking control of the solar cell.
Even with such an “external type” configuration, the object of the present invention can be completely achieved. (Embodiment 3) FIG. 3 shows Embodiment 3 of the present invention. In the third embodiment, the charging / discharging interface 71 is a simple switch, and as the secondary battery 72, a NiCd battery that withstands fairly violent charging / discharging is adopted. The third embodiment is characterized in that the charging / discharging interface 71 is a simple switch, so that the system can be constructed at an extremely low cost. That is, when the power reception voltage rises, the switch made up of the charge / discharge interface 71 is closed to charge the storage battery. At this time, the output of the inverter 2 is throttled so that the received voltage decreases, and at the same time, the output voltage of the solar cell array 1 increases and the amount of charge in the battery increases. Further, when the power receiving voltage is lowered and the output of the solar cell array 1 is reduced, the energy is discharged from the secondary battery 72. That is, the output of the inverter 2 is increased to absorb energy from the battery.

In this method, unless the charging voltage of the secondary battery 72 is selected near the maximum operating point of the solar cell, the efficiency of the system may be reduced or the life of the secondary battery 72 may be shortened. . Therefore, it is necessary to carefully select the secondary battery 72. Further, for example, since the lithium secondary battery requires severe charge / discharge management, it should not be used in the case of the third embodiment.

[0027]

As described above, the solar power generation system of the present invention has the following effects. Even when the voltage of the power system is high, the output of the solar cell is effectively used while maintaining the voltage at the receiving end normally. (1) System When the voltage of the system is high, electricity is stored in the power storage means, so that the output voltage of the inverter is prevented from exceeding the legal value. As a result, the solar cell can be operated at the maximum output point while maintaining the output voltage of the solar power generation system within the legal value, and therefore solar energy can be effectively used. (2) Since the phase reactive power is not injected into the power system to maintain the voltage, it is not necessary to increase the capacity of the inverter. Further, since the phase-advancing reactive power is not injected, the power factor does not decrease and the distribution line is not burdened. Furthermore, since it is not necessary to increase the output current, the overcurrent protection function is not adversely affected.

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

FIG. 4 is an explanatory diagram of changes in the received voltage during power reception and reverse power flow in the solar power generation system.

FIG. 5 is a graph showing an example of voltage fluctuation data in a power system.

FIG. 6 is an explanatory diagram showing the principle of the DC / DC converter that constitutes the charge / discharge interface used in the embodiment.

FIG. 7 is an explanatory diagram showing an example of the configuration of an inverter used in an example.

FIG. 8 is a graph showing the operation of the solar power generation system of the present invention.

FIG. 9 is a graph showing the operation of a conventional photovoltaic power generation system.

FIG. 10 is an explanatory diagram showing a conventional example of a solar power generation system.

[Explanation of symbols]

 1 Solar Cell Array 2 Inverter 3 General Load 4 Interconnection Protection Device 5 Commercial Power System 6 Control Device 7 Storage Device 71 Charge / Discharge Interface 72 Storage Battery 11 Customer 12 Distribution Line Impedance 13 Commercial Power System 31 DC Power Supply 32 Switching Device 33 Inductance 34 Diode 35 Capacitor 36 Load VR Received voltage VS System voltage

Claims (2)

[Claims] 1. A solar power generation system having a solar cell, an inverter that converts direct current generated by the solar cell into alternating current, and a storage means, and the output of the inverter is connected to a power system, wherein the power system The photovoltaic power generation system is characterized in that the power storage means stores the power generation energy of the solar cell when the voltage of V exceeds a predetermined value. 2. The storage means is connected to the output side of the inverter, and the storage means is a secondary battery,
The photovoltaic power generation system according to claim 1, further comprising an AC / DC converting unit connected to the secondary battery and the power system.