JP2710736B2 - Power generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power generator , and more particularly to a power generator 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 rapidly increased due to global warming and radioactive contamination due to a nuclear accident. Under these circumstances, solar cells are expected from all over the world as renewable and inexhaustible clean energy sources. By the way, solar cells can of course only extract energy during the day when the sun is out . Therefore, some auxiliary means are required to use the solar cell as a stable energy source.

[0003] The best method for such auxiliary means is
The DC output from the solar cell is converted into alternating current by inverter,
In this method, the AC conversion output is connected to a power system such as a commercial AC system that we use every day, that is, used together with the power system. This method is considered to be a favorite for the spread of the solar cell system, since if the solar cell is installed on the roof, no land for installation is required. In Japan, the development of the legal system has recently been promoted, and the grid interconnection system as described above has become practically available. FIG. 10 shows an example of this type of power generation device .

[0004] In FIG. 10, the DC power outputted a plurality of solar cells from the solar cell array 1 made by combining the series-parallel is converted to AC power via the inverter 2, the general supply load 3 And the system interconnection protection device 4. Furthermore the load 3 and the inverter 2, the grid interconnection device 4
The commercial power system 5 is connected via the. Inverter
Numeral 2 receives commands such as control for tracking the maximum output point of the solar cell and control for setting the power factor to 1 by the control device 6. this
In the power generation apparatus, power consumption of the general supply load 3 is inverter 2
When the output is smaller than the output, the surplus power flows back to the commercial power system 5. In addition, the power consumption of the general load 3
When the output is larger than the output of the power supply 2, the shortage is supplied from the commercial power system 5. By using the power generation device having such a configuration, the solar cell power generation equipment can be used as a stable energy source.

[0005] Since an abnormality in the power system has a great effect on the entire society, the frequency, voltage, harmonic distortion, etc. of the commercial power system are strictly maintained and managed by the power company.
For example, in a 100V system used in ordinary households, the voltage is defined as 101 ± 6V by the Electricity Business Law. As a matter of course, the power generator that flows backward into the system must not deviate from the voltage range. In addition, technical standards such as maintaining the power factor close to 1 and suppressing the harmonic current distortion factor to 5% or less are defined for the power generator connected to the power system .

[0006]

By the way, in order to connect the commercial power system and the generator as described above, it is, of course, necessary to connect a distribution line between them. Further, since the distribution line has impedance, it is inevitable that a voltage drop occurs during power transmission. For example, FIG.
In such a system, since the distribution line impedance 12 exists between the commercial power system 13 and the customer 11, the receiving voltage VR of the customer 11 becomes the system voltage V of the commercial power system 13.
It will be lower than S. Therefore, the commercial power system 13
Is set slightly higher in consideration of the voltage drop due to the distribution line impedance 12. For example, the low voltage side output of the pole transformer is set to 105 V, and the receiving voltage of the consumer becomes 105 V when there is no load.
Then, when power is sent from the photovoltaic power generation system to the power system, the distribution line impedance suffers and the voltage at the customer receiving end exceeds 105 V.
For example, assuming that the received voltage becomes 101 V when 30 A is consumed, if 30 A is reversely flowed, the voltage drop is applied in reverse, and it becomes 109 V, exceeding the allowable voltage range.

[0007] The simplest method for preventing such inconvenience on the power generation device side is a method of suppressing 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 thrown away.

As a second method, there is an advanced phase power injection method proposed by the Central Research Institute of Electric Power Industry. Although this method is effective, it is necessary to increase the output apparent power, must above up without the capacity of the inverter, to which may result in a negative impact on the order overcurrent protection function, also be appreciated However, the power factor is lowered. 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 3KW
Is about 30 A, so the overcurrent protection function should be activated at about 33 A, which is a 10% increase. Also, the power factor at this time drops to about 0.7.
For this reason, there is a possibility that a larger current flows through the distribution line than the design, and this places a burden on the distribution line.

Some complicate the above voltage maintenance problem. That 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 substations and the like. For this reason, the voltage of the power system is not constant, but is constantly changing. FIG. 5 shows the measured values of the voltage in the power system for one day measured by the inventor. At the point indicated by the arrow A, the voltage of the system has reached the legal upper limit of 107 V. At this point, it is clear that when power is supplied to the system, the voltage exceeds the upper limit.

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

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

[0012]

The power generation device of the present invention has a large thickness.
A solar cell and convert the DC output of the solar cell into an AC output,
First inverter connected to a power system having a load
And a second converter for converting an AC output from the first inverter.
And the output from the second inverter is stored.
And an output from the first inverter.
When the value exceeds a predetermined value, the signal from the first inverter
AC output is input to the second inverter and the input is converted
And then charging the storage means with the output from the conversion.
And the output from the first inverter is the maximum power
The first inverter is controlled so that point-following control is performed.
And an output value from the first inverter is equal to or less than the predetermined value.
At times, the power stored in the power storage means is discharged, and
Converting the electric power of the electric power by the second inverter ;
It is characterized by having means for outputting to a system.

[0013]

[Action] In the power generation apparatus of the present invention, when the voltage of the output voltage, that is the receiving end of the inverter has reached the legal limit, that began stored electrical energy in the power storage means. For this reason, the power flowing backward to the power system is reduced, and a voltage rise can be prevented. When the voltage of the power system drops, the stored electricity is discharged, and the stored energy is output to the power system. Therefore, at the time of the power storage, it is not necessary to suppress the output of the solar cell, so that solar energy can be effectively used.

Therefore, according to the present invention, solar energy can be effectively used while maintaining the legal voltage range. Since a large amount of phase leading reactive power does not need to flow into the power system, there is no adverse effect on the overcurrent protection function and the like, and no load is imposed on the distribution line. In particular, the invention of the present invention
The configuration using power generators is
Is effective without destroying existing power generators
While improving solar energy utilization efficiency.
You. Therefore, inexpensive introduction is possible. Also, electricity storage
Solar cell or first invar even while charging the stage
Can be replaced for maintenance.

In the present invention, since the control method is such that the power is stored in the power storage means when the voltage of the power system is high, the secondary battery or the like used for the power storage means may have a relatively small capacity, and may have a large capacity and an expensive capacity. It is not necessary to use a thing.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter , the present invention will be described in detail based on embodiments and reference examples . ( Reference Example 1 ) FIG. 1 shows a power generator according to Reference Example 1 of the present invention. DC output generated from the solar cell array (solar cell) 1 is connected to storage means 7 and the inverter 2. The power storage means 7 includes a charge / discharge interface 71 and a secondary battery 72. The role of the charging / discharging interface 71 is to perform voltage matching between the secondary battery 72 and the solar cell array 1 and to control charging and discharging 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 for charging the secondary battery 72 is also substantially determined by the type of the battery, the remaining amount of the battery, the temperature, and the like. Of course, the number of series solar cells and secondary batteries should be devised at the time of design so that the difference between these two voltages is as small as possible. Since the change in the charging voltage of a secondary battery such as a lead battery is small, matching is difficult. Therefore, even if these batteries are directly connected without voltage matching, the purpose of the present invention can be achieved, but there is a slight reduction in efficiency due to voltage mismatch.

The charge / discharge interface 71 is usually
Both the voltage step-up and step-down is composed of DC / DC converter capable. DC /
The principle diagram of a DC converter shown in FIG. 6. By opening and closing the switch 32, magnetic energy is stored in the inductance 33 and 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 power generation device of this example , the control device 6 controls the charge / discharge interface 71.
As the secondary battery 72, a nickel-cadmium battery, a lead battery, a lithium secondary battery, a nickel-metal hydride battery, or the like can be used.

[0018] FIG. 7, the inverter to be used of Reference Example 1
2 is an example. The DC power output from the solar cell array 1 is passed through a DC filter 21 to a switching unit 22.
And is connected to the power system through the AC filter 23. Here, the DC filter 21 is for compensating for a sudden change in output due to a sudden change in solar radiation or the like, 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 the DC input between positive and negative and supplying the load to the load, and is a part that plays a role of DC-AC conversion. Various methods have been proposed for the DC-AC conversion part, but a voltage-type current control PWM method is mainly used for low-voltage system interconnection. This method is characterized in that an output waveform with very little harmonic distortion can be obtained. The elements used in the switching unit include:
Power transistor, power MOSFET, IGBT,
There are SIT, thyristor, GTO and the like. Currently, several KW
Power transistor, MOSFE
A self-extinguishing type, such as T or IGBT, capable of increasing the switching frequency is used.

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

[0020] the control device 6, controls the charge and discharge interface 71 and inverter 2 is made. The control device 6, the system output voltage and current of the solar cell array 1, the output current in the <br/> bar motor 2, the output voltage, power factor, voltage, current or residual quantity of the secondary battery 72 as input information Take control of the whole. Particularly important information in the present invention, the output voltage of the in-<br/> bar motor 2, and the output voltage or the output current of the solar cell array 1, a remaining amount of battery. At least this 4
Without this information, the object of the present invention cannot be achieved. The control device 6 comprises a microcomputer and its peripheral interface elements. For example,
As a microcomputer, Z80, 8086, V30, 6800
0 and the like, and the peripheral interface includes a parallel interface, a DMA, an A / D converter, and the like. In the first embodiment , the control system is constituted by a digital control system, but there is no problem even if the control system is constituted by an analog system. 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 enters 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, to open and close the switching means inverter 2,
DC / AC conversion is performed, and energy is discharged to the commercial power system 5. In this state, the maximum output is extracted from the solar cell array 1 by changing the duty ratio of the switching means so that the output power of the solar cell array 1 becomes maximum. At this time, the phase of the output current is controlled so as to match the output voltage phase, and the power factor is kept substantially at 1.

[0022] At this point, the output voltage of the inverter 2 if within legal value, to continue the operation. In the case where the output voltage of the inverter 2 exceeds the legal value, the control unit 6 issues a charge command to the charging and discharging interface 71, to start charging of the secondary battery 72 which had been allowed to advance discharged. At this time, lower the output power of the inverter 2 while maintaining the maximum output point of the solar cell array 1, i.e., voltage to synchronize the switching means inverter 2 and charge and discharge interface 71 so down to the legal value control I do. Furthermore, if not reduced to legal voltage in the synchronous control, to stop the operation of the inverter 2, revert to all charge the output of the solar cell array 1. Such a charging operation is continued until the system voltage drops by several volts from the legal upper limit. 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 5 V, though it depends on the power flowing backward. Since the voltage of the power system changes every moment and the amount of solar radiation fluctuates, the state where the voltage is high does not last so long, and is at most within 30 minutes. Therefore, a relatively small capacity of the secondary battery used in the present invention is sufficient, for example, a capacity of 500 Wh for a solar cell having a maximum output of 1 kW. This corresponds to one automobile battery when the depth of discharge is 100%. As a matter of course, the secondary battery has a very short life at a depth of discharge of 100%, and therefore requires a little more capacity, but it is clear that a huge battery is not required. Note that when the battery reaches a fully charged state during the charging operation and the voltage of the system has not decreased, the charging operation is also stopped, and the system enters a standby state until the system voltage decreases.

Meanwhile, lower the incoming voltage, and when the output power from the solar cell array 1 is sufficiently small, feeds DC power to the inverter 2 through the discharge interface 71 from the secondary battery 72 that was just charged . In <br/> bar motor 2, the combined output from the output and the rechargeable battery 72 of the solar cell array 1, thereby backward flow power to the commercial power system 5. This operation is continued until the remaining amount of the secondary battery 72 becomes empty. However, if the receiving voltage exceeds the legal upper limit during operation, the charging operation starts again.

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

On the other hand, FIG. 9 shows the operation of a conventional power generation device of the type that suppresses the power generated from a solar cell (solar cell array). In FIG. 9, when the receiving voltage shown by the solid line A rises, the output of the solar cell shown by the solid line B is suppressed, and the output that the solar cell shown by the diagonal line can output is discarded. Recognize. In contrast, the reference example
In the power generation device of No. 1 , the energy corresponding to the hatched portion in FIG. 9 is stored in the secondary battery.

Embodiment 1 FIG. 2 shows a system configuration of Embodiment 1 of the present invention. The feature of this first embodiment is that the charge and discharge interface 71 and the secondary battery 72 is arranged on the output side of the inverter 2. In such a configuration, the charge / discharge interface 7
1, there is a need to have the functionality of the inverter. In this configuration, the power storage unit 7 may have another independent control system and the inverter 2 for a solar cell. That is, conventional power generation equipment
There is a feature that the power generation device of the present invention can be externally attached to a device . That is, the function of monitoring the receiving voltage and the function of controlling the charge / discharge are provided by the charge / discharge interface 71.
To have, inverter 2 the maximum power point tracking control of solar cells
May be provided to the control device 6. The object of the present invention can be completely achieved even with such an “external type” configuration.

( Reference Example 2 ) FIG. 3 shows Reference Example 2 of the present invention. In the reference example 2 , the charging / discharging interface 71 is a simple switch, and a nickel-cadmium battery that can withstand quite rough charging / discharging is used as the secondary battery 72. In the reference example 2 , since the charge / discharge interface 71 is a simple switch, there is a feature that the power generation device can be configured at very low cost.
That is, when the receiving voltage rises, charges the battery by closing a switch consisting of the charge and discharge interface <br/>-safe E over scan 71. At this time, as the receiving voltage drops inverter 2
Is reduced, and at the same time, the output voltage of the solar cell array 1 increases, and the amount of charge to the battery increases. Also, when the receiving voltage decreases and the output of the solar cell array 1 decreases,
The energy is discharged from the secondary battery 72. That is, by raising the output of the in-<br/> bar motor 2, suck up energy from the battery.

In this method, if the charging voltage of the secondary battery 72 is not selected near the maximum operating point of the solar cell, the efficiency of the power generator is reduced or the life of the secondary battery 72 is shortened. Sometimes. Therefore, it is necessary to carefully select the secondary battery 72. Further, for example, since a lithium secondary battery requires severe charge / discharge management, it is better not to use it in the case of Reference Example 2 .

[0029]

As described above, according to the power generator of the present invention, the following effects can be obtained. 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.

[0030] (1) By storing electricity in the electric storage means when the voltage of the system the system is high, the output voltage of the inverter is prevented from exceeding the legal values. Thereby, the solar cell can be operated at the maximum output point while maintaining the output voltage of the power generation device within the legal value, so that the solar energy can be used effectively.

[0031] (2) Since there is no injecting fast reactive power to the power system for voltage maintenance, there is no need to increase the <br/> capacity inverter. In addition, since the leading phase reactive power is not injected, the power factor does not decrease and the distribution line is not burdened. Further, since the output current does not need to be increased, the overcurrent protection function is not adversely affected.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of a power generator according to Embodiment 1 of the present invention.

FIG. 3 is an explanatory diagram of a power generator according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a change in received voltage at the time of power reception and at the time of reverse power flow in the power generation device .

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

6 is an explanatory view showing the principle of the Examples and the DC / DC converter constituting the charging and discharging interface used in Reference Example.

7 is an explanatory diagram showing an example of <br/> configuration of inverter used in the Examples and Reference Examples.

FIG. 8 is a graph showing the operation of the power generator according to the present invention.

FIG. 9 is a graph showing the operation of a conventional power generator .

FIG. 10 is an explanatory diagram showing a conventional example of a power generator .

[Explanation of symbols]

1 the solar cell array, 2 inverter, 3 OTC load, quadruple system protection device 5 commercial power system, 6
Control device , 7 power storage means , 71 charge / discharge interface , 72 storage battery , 11 consumer , 12
Distribution line impedance , 13 commercial power system , 31
DC power supply , 32 switching means , 33 inductance , 34 diode , 35 capacitor , 36 load , VR receiving voltage , VS system voltage .

Claims (2)

(57) [Claims] 1. A solar cell and a DC output of the solar cell are exchanged.
To a power output and connected to a power system with a load.
An inverter and an AC output from the first inverter
And a second inverter for converting the
Power storage means for storing the output of the first inverter.
When the output value from the data exceeds a predetermined value, the first
AC output from the inverter is input to the second inverter
Converting the input, and then converting the output from the
Charging the means, from the first inverter
So that the output of the first power point is controlled to follow the maximum power point.
Control the inverter, and the output value from the first inverter is
When the voltage is equal to or less than the predetermined value, the electric power charged in the power storage unit is
Discharging, and discharging the electric power by the second inverter.
Conversion means for output to the power system.
Power generator Wherein said electrical storage means, nickel-cadmium battery, lead battery, a lithium battery, power generating apparatus according to claim 1, wherein the at least one of the nickel hydrogen battery.