JPH08251832A - Charging method and charging device using solar cell - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent overcharging of a secondary battery and extend its life, while maximizing use of the output of the solar cell and enabling efficient charging. [Configuration] DC and current and voltage output from the solar cell 1
The voltage Vout converted by the DC / DC converter 4 is compared with the preset voltage VB by the comparator 7, and when VB≥Vout, the maximum charging current flows through the storage battery 2. Vref is commanded from the maximum charging current controller 8 to the DC / DC converter 4, and Vout> VB
When it becomes, a constant floating voltage V
The command is given to charge the storage battery 2 at f.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, a solar power generation system and the like, and a charging method for charging a secondary battery such as a lead storage battery using a solar cell as a power source and charging used for implementing the method. It relates to the device.

[0002]

2. Description of the Related Art As this type of charging method, conventionally, the following two methods are known. One of them is
It has a circuit configuration as shown in FIG. That is, the solar cell 1 is used as a power source, the output voltage Vs of the solar cell 1 is kept constant, and a current Is that is sufficient to compensate for the self-discharge of the secondary battery 2 is continuously supplied to the secondary battery 2 through the backflow prevention diode 3. It is a floating charging method for charging. The other one is to maximize the output of the solar cell 1, and among the current-voltage characteristics of the solar cell shown by the solid line in FIG. 16, the voltage Va at which the electric power generated from the solar cell is maximum. And a voltage such that the maximum power point represented by the intersection point P of the current-voltage characteristics under the open-circuit voltage Vop of the storage battery shown by the two-dot chain line in FIG. It is a method of charging.

[0003]

All of the above-mentioned conventional charging methods charge the storage battery at a constant voltage, so that the characteristics of the solar cell change due to environmental changes such as illuminance fluctuations and temperature fluctuations. At this time, since the optimum charging voltage also changes, the output of the solar cell cannot be used for charging to the maximum extent, resulting in a decrease in charging efficiency. Further, according to the latter method, since the charging rate is always increasing, there is a problem that if the battery is continuously charged as it is, it will be overcharged, which will have a great adverse effect on the life of the storage battery.

The present invention has been made in view of the above circumstances, and prevents overcharge of the secondary battery and prolongs its life,
It is an object of the present invention to provide a charging method and a charging device using a solar cell, which can perform efficient charging by always using the maximum output of the solar cell.

[0005]

In order to achieve the above object, a charging method using a solar cell according to the invention of claim 1 compares a voltage across a secondary battery with a preset voltage, When the set voltage is large according to the comparison result, the secondary battery is controlled so that the maximum current flows, and the secondary battery is charged with the maximum current, and the voltage across the secondary battery is large according to the comparison result. In this case, the secondary battery is switched to a mode in which the secondary battery is charged at a constant floating voltage.

Here, it is preferable that the floating voltage is set to a voltage that complements the self-discharge of the secondary battery.

Further, in a charging device using a solar cell according to the invention of claim 3, the power output from the solar cell is converted into a voltage,
A converter for converting into a current, a voltage detector and a current detector for detecting an output voltage and an output current from the converter, and a comparator for comparing the voltage detected by the voltage detector with a preset voltage. And a maximum current control unit for controlling the current flowing through the secondary battery to be maximum, and a floating voltage command unit for instructing the voltage when the secondary battery is charged to be a floating voltage, the above comparison A mode in which the maximum current control unit issues a command to the conversion unit to charge the secondary battery with the maximum current based on the comparison result in the device, and the floating voltage command unit issues an instruction to the conversion unit to provide a constant floating voltage. The charging mode switching unit automatically switches to a mode for charging the secondary battery.

Further, in a charging device using a solar cell according to the invention of claim 4, a converter for converting electric power output from the solar cell into a voltage and a current, and an output voltage and an output current from the converter. A voltage detecting unit and a current detecting unit for detecting, a comparator for comparing the voltage detected by the voltage detecting unit with a preset voltage, and the secondary battery is charged at the maximum power point of the solar cell. A maximum power tracking control unit that commands a voltage to the conversion unit, and a floating voltage command unit that commands the voltage when the secondary battery is charged to be a floating voltage,
Based on the comparison result in the comparator, the maximum power tracking control unit commands the conversion unit to charge the secondary battery at the maximum power point of the solar cell, and the floating voltage command unit commands the conversion unit. The charging mode switching unit automatically switches to a mode in which the secondary battery is charged at a constant floating voltage.

In the charging device of the above-mentioned claim 3 and claim 4, it is of course preferable that the floating voltage of the floating voltage command section is set to a voltage that complements the self-discharge of the secondary battery. Is.

[0010]

According to the inventions of claims 1 and 3, while comparing the voltage across the secondary battery and the preset voltage,
When the voltage across the secondary battery is smaller than the set voltage based on the comparison result, it is possible to perform efficient charging by setting the mode in which the output of the solar battery is used as the maximum charging current, When the voltage across the secondary battery becomes higher than the set voltage, the charging mode is switched to a constant floating voltage to prevent overcharging and prolong the life of the secondary battery.

Here, in particular, if the floating voltage is set to a voltage that compensates for the self-discharge of the secondary battery, overcharge can be prevented and the secondary battery can always be kept in a fully charged state. It is possible.

Further, according to the invention of claim 4, the maximum power point of the solar cell is made to follow the output of the solar cell even when the characteristics of the solar cell change due to environmental changes such as illuminance fluctuation and temperature fluctuation. It is possible to use the maximum charging current and always perform efficient charging, while preventing overcharging and extending the life of the secondary battery.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a configuration diagram of Embodiment 1 of a charging device for carrying out a charging method using a solar cell according to the present invention, in which 1 is a solar cell and 2 is a secondary battery. A certain storage battery, 4 is a DC / DC converter (conversion unit) for converting the voltage and power output from the solar cell 1 into a current and a voltage, and 5 is a current for detecting the output current Iout of the DC / DC converter 4. A sensor (current detector), 6 is a voltage sensor (voltage detector) for detecting the output voltage Vout of the DC / DC converter 4, and 7 is an output voltage Vout detected by the voltage sensor 6 and a preset voltage VB. The comparator 8 compares the input voltage Vin to the DC / DC converter 4 and the input current Iin to a voltage Vref that allows the maximum charging current Iout to flow to the storage battery 2, and controls the voltage Vref to the DC / DC. Comba Maximum charging current control unit for commanding the motor 4, 9 floating voltage Vf of the DC / D, which is set to a constant voltage on the order Nau complement the self-discharge of the storage battery 2
The floating voltage command unit 10 which commands the C converter 4 commands the voltage Vref from the maximum charging current control unit 8 to the DC / DC converter 4 based on the comparison result of the comparator 7 to operate the storage battery 2 at the maximum current. The charging mode (hereinafter referred to as A mode) and the floating voltage Vf from the floating voltage command unit 9
Is a charge mode changeover switch (mode changeover unit) for automatically switching to a mode (hereinafter, referred to as B mode) for instructing the DC / DC converter 4 to charge the storage battery 2. Incidentally, 3 in FIG. 1 is a backflow prevention diode.

As shown in FIG. 2, the storage battery 2 is composed of a battery portion 2a and an internal resistance R (which changes depending on the flowing current), and the actual charging voltage VA of the storage battery 2 is
Is the open circuit voltage V actually charged in the battery portion 2a.
It is represented by the sum of op and the voltage drop at the internal resistance R. Therefore, the charging voltage VA of the storage battery 2 increases as the charging current IA increases, as shown in FIG. 3, and the current-voltage characteristic of the storage battery 2 varies depending on the magnitude of the charging rate.

Next, the charging operation in the A mode and the B mode by the charging device having the above structure will be described. Mode A: The output voltage Vout detected by the voltage sensor 6 and the preset voltage VB are compared by the comparator 4, and when the comparison result shows that VB ≧ Vout, the charging mode changeover switch 10 causes the DC / DC. The maximum charging current control unit 8 is connected to the converter 4 to enter the A mode. By the way, as shown in FIG.
The input voltage Vin and the input current Iin to the DC / DC converter 4 are converted by the DC / DC converter 4, and the power is V
If out and Pout are used, the following relationship is established. Vout = DVin (1) Pout = ηPin (2) where η is the efficiency of the DC / DC converter 4 (0 <η <
1) and D are ratios (voltage conversion ratios) of the input voltage Vin and the output voltage Vout. From the above equations (1) and (2), the input current I
The relationship between in and the output current Iout is as follows: Iout = (η / D) Iin (3) When the relationship between the output voltage Vout and the output current Iout is shown by a glass, the result is as shown in FIG. Here, 3
The value of type D (D1>D2> D3) was used, and the efficiency was η = 1.

If the current Iin and the voltage Vin input from the solar cell 1 to the DC / DC converter 4 have the characteristics shown in FIG. 5A, in order to convert this into the current-voltage characteristics seen from the output side. For this purpose, it is necessary to map the current and the voltage by using (b) and (c) of FIG. The intersection (points A, B, X) of the current-voltage characteristic of the output side and the current-voltage characteristic of the storage battery 2 becomes the operating point, and the charging voltage-charging current characteristic as shown by the dotted line in (d) of FIG. Becomes here,
By changing the value of the voltage conversion ratio D of the DC / DC converter 4 to a large or small value, the current-voltage characteristic on the output side changes, and the operating point (A, B, X) also changes in the direction of the arrow accordingly. . That is, as shown in FIG. 6, as the value of D increases, the characteristics on the output side shift in the direction in which the current decreases and the voltage increases, and the relationship between the value of D and the charging current at this time is shown in FIG. It becomes like 7. From this, it can be seen that there is only one value at point D (D2 in FIG. 7) that maximizes the charging current. In the A mode, charging is always performed at the maximum current by causing the charging current at the operating point C to flow.

In order to perform the charging in the A mode as described above, the maximum charging current control unit 8 performs a search operation for the maximum charging current. The internal structure of the maximum charging current control unit 8 used for this purpose. As an example, the one shown in the block diagram of FIG. 8 can be considered. That is, the temporal difference between the output voltage Vout and the output current Iout detected by the voltage sensor 6 and the current sensor 5 is obtained, and the obtained output voltage difference ΔVout and output current difference ΔIou are obtained.
By inputting t, the maximum charging voltage difference ΔVopt is calculated by a predetermined algorithm, the output voltage Vout is added to the maximum charging voltage difference ΔVopt to obtain the maximum charging voltage Vopt, and this is multiplied by the predetermined conduction ratio Kα. The voltage Vref is commanded to the DC / DC converter 8 so that the storage battery 2 can be charged with the maximum charging current Iout.

B mode: Output voltage (charging voltage) V detected by the voltage sensor 6 as the charging in the A mode progresses.
When the result of comparison between out and the preset voltage VB by the comparator 4 becomes Vout> VB, the charging mode changeover switch 10 automatically switches to the B mode, and the floating voltage command section 9 switches to the DC / DV converter 4. The floating voltage Vf set to a constant voltage that compensates for the self-discharge of the storage battery 2 is commanded. The state of charging in this B mode is shown in FIG.
Since the charging rate becomes high at this time, the charging voltage-charging current characteristic of the storage battery 2 becomes a curve. Therefore, the charging current can be greatly reduced by lowering the set value of the floating voltage Vf below the set voltage VB in the A mode.

FIG. 10 shows changes in the terminal voltage of the storage battery 2 when the battery is charged in the above A mode and B mode.
That is, at the time (T1) when the charging in the A mode is started and the voltage across the storage battery 2 reaches the set voltage VB shown at the point P (T1),
The charging is switched to the B mode and the charging is continued at the floating voltage Vf. As a result, the output of the solar cell 1 is maximized as the charging current and efficient charging is performed while the set voltage VB
By changing over to the charging with the floating voltage when the temperature reaches, the overcharge can be prevented and the life of the storage battery 2 can be extended.

Embodiment 2 FIG. 11 is a configuration diagram of Embodiment 2 of a charging device for carrying out a charging method using a solar cell according to the present invention. In FIG. 11, 1 to 7, 9 and 10 are Since it has the same configuration as that of the first embodiment shown in FIG.

In FIG. 11, the difference from the first embodiment of FIG. 1 is that instead of the maximum charging current control unit 8, the storage battery 2 is used.
Is the voltage Vre at which the solar cell 1 is charged at the maximum power point
This is the point that the maximum power follow-up control unit 12 that commands f to the DC / DC converter 4 is used. This maximum power tracking control unit 1
As an example of the internal configuration of No. 2, the one shown in the block diagram of FIG. 12 can be considered. That is, the output power Pout is calculated from the output voltage Vout and the output current Iout detected by the voltage sensor 6 and the current sensor 5, and the output power Pou is calculated.
The time difference between t and the output voltage Vout is calculated, and the calculated output power difference ΔPout and output voltage difference Δ
Vout is input and the maximum charging voltage difference ΔVopt is calculated by a predetermined algorithm. The maximum charging voltage difference ΔVopt is added to the output voltage Vout to obtain the maximum charging voltage Vopt.
This is multiplied by a predetermined conduction ratio Kα to instruct the DC / DC converter 8 or the solar cell 1 to generate a voltage Vref capable of charging the storage battery 2 with the maximum charging current Iout.

Also in the case of the second embodiment, as in the first embodiment,
There are two types of charging modes, A mode and B mode. Next, the operation of each of these charging modes will be described. A mode; First, consider the current-voltage characteristics of the storage battery 2. The relational expression of charging current-charging voltage is IA = 1 / R (VA-Vop) (4) VA = RIA + Vop where Vop is the open voltage of the storage battery, R is the internal resistance, and charging power PA is , PA = IA VA, then PA = RIA ² + IA Vop = IA (RIA + Vop) (5) A graphical representation of this relationship is as shown in FIG. This graph monotonically increases if the charging current is positive, so that if the electric power input to the storage battery 2 is maximum, the charging current of the storage battery 2 is also maximum. Further, when the power input to the DC / DC converter 4 is the maximum, the output power is also the maximum. In other words, P2 = ηP1 (6) where P1: input voltage P2: output power η: efficiency of DC / DC converter By always obtaining the maximum power point from the solar cell 1, The maximum current can always flow through the storage battery 2.

Then, how is the solar cell 1
Whether or not the storage battery 2 is charged at the maximum power point will be described. Basically, the voltage −
Instead of the current characteristics, the voltage-power characteristics as shown in FIGS. 14A to 14D may be used. Here, by changing the value of the voltage conversion ratio D of the DC / DC converter 4 of FIG. 14C as D1 to D3, the voltage-power characteristic on the output side changes, and as a result, the operating point (A, B,
C) also changes. By setting the value C of the output power at this operating point to be the maximum, the storage battery 2 can be charged at the maximum power point of the solar cell 1.

B mode: The charging in this case is the same as in the first embodiment, and the floating voltage command unit 9 sets the DC / DV converter 4 to a constant voltage to a level that compensates for the self-discharge of the storage battery 2. Command the voltage Vf.

As described above, the output voltage (charging voltage) Vout detected by the voltage sensor 6 and the preset voltage VB
When the result of comparison by the comparator 4 with VB ≥ out, charging is performed in the A mode, and when Vout> VB, charging mode switching switch 10 is switched to perform charging in the B mode. The maximum power point of the solar cell 1 is always tracked even for environmental changes such as fluctuations in illuminance and temperature, and efficient charging is performed while overcharging is prevented, and the life of the storage battery 2 is extended. It can be achieved.

[0026]

As described above, claim 1 and claim 3 are as follows.
According to the invention, when the voltage across the secondary battery is smaller than the set voltage based on the comparison result between the voltage across the secondary battery and the preset voltage, the output of the solar cell is maximized to the charging current. Although it is possible to perform efficient charging with the mode used as, when the voltage across the secondary battery becomes higher than the set voltage, by switching to the charging mode with a constant floating voltage, The effect of preventing overcharge and extending the life of the secondary battery can be achieved.

In particular, when the floating voltage is set to a voltage that complements the self-discharge of the secondary battery, it is possible to prevent the overcharge and always keep the secondary battery in a fully charged state.

According to the invention of claim 4, the maximum power point of the solar cell is made to follow the change of the characteristic of the solar cell due to the change of environment such as the change of illuminance and the change of temperature, and the output thereof is changed. It is possible to use the maximum charging current and always perform efficient charging, but it is possible to prevent overcharging and prolong the life of the secondary battery.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a charging device for carrying out a charging method using a solar cell according to the present invention.

FIG. 2 is a diagram showing the internal circuit configuration of the storage battery according to the first embodiment.

FIG. 3 is a current-voltage characteristic diagram of the storage battery according to the first embodiment.

FIG. 4 is an explanatory diagram of input / output relationships of the DC / DC converter according to the first embodiment.

FIG. 5 is the output voltage after voltage conversion in the first embodiment-
It is an output current characteristic diagram.

FIG. 6 is a relationship diagram between output-side current-voltage characteristics and charging voltage-charging current characteristics in the first embodiment.

FIG. 7 is a relationship diagram between a voltage conversion value and a charging current according to the first embodiment.

FIG. 8 is a block diagram showing a configuration of a maximum charging current control unit according to the first embodiment.

FIG. 9 is a current-voltage characteristic diagram at the time of charging in the B mode according to the first embodiment.

FIG. 10 is a time change diagram of the terminal voltage of the storage battery during charging according to the first embodiment.

FIG. 11 is a configuration diagram of a second embodiment of a charging device for carrying out a charging method using a solar cell according to the present invention.

FIG. 12 is a block diagram showing a configuration of a maximum power tracking control unit in the second embodiment.

FIG. 13 is a charging current-power characteristic diagram of the storage battery at the time of charging in the A mode according to the second embodiment.

FIG. 14 is an output voltage-power characteristic diagram after voltage conversion according to the second embodiment.

FIG. 15 is a circuit configuration diagram of a charging device used for implementing a conventional floating charging method.

FIG. 16 is a current-voltage characteristic diagram of a solar cell and a secondary battery for explaining another conventional charging method.

[Explanation of reference symbols] 1 solar cell 2 secondary battery 4 DC / DC converter (example of conversion section) 5 current sensor (example of current detection section) 6 voltage sensor (example of voltage detection section) 7 comparator 8 maximum charging current Control unit 9 Floating voltage command unit 10 Charging mode changeover switch (example of mode changing unit) 12 Maximum power tracking control unit VB set voltage Vf Floating voltage

Claims (5)

[Claims] 1. A charging method for charging a secondary battery using a solar battery as a power source, wherein the voltage across the secondary battery is compared with a preset voltage, and when the comparison result shows that the set voltage is large, The secondary battery is controlled so that the maximum current flows, and the secondary battery is charged with the maximum current, and,
According to the comparison result, when the voltage across the secondary battery is large, the charging method using a solar cell is characterized by switching to a mode in which the secondary battery is charged with a constant floating voltage. 2. The charging method using a solar cell according to claim 1, wherein the floating voltage is set to a voltage that compensates for self-discharge of the secondary battery. 3. A charging device configured to charge a secondary battery using a solar cell as a power source, the conversion section converting the electric power output from the solar cell into voltage and current, and the conversion section. Voltage detector and current detector for detecting the output voltage and output current, a comparator for comparing the voltage detected by the voltage detector with a preset voltage, and the current flowing through the secondary battery is maximized. To control the maximum current control unit, a floating voltage command unit to command the voltage when the secondary battery is charged to be a floating voltage, and the maximum current control based on the comparison result of the comparator. Section to instruct the converter to charge the secondary battery at the maximum current and the floating voltage command section to instruct the converter to charge the secondary battery at a constant floating voltage. Charge mode to switch to Charging devices using a solar cell characterized by comprising a changing unit. 4. A charging device configured to charge a secondary battery using a solar cell as a power source, the conversion section converting the electric power output from the solar cell into voltage and current, and the conversion section. Of the output voltage and the output current of the voltage detection unit and the current detection unit, a comparator for comparing the voltage detected by the voltage detection unit and a preset voltage, the secondary battery is the maximum power of the solar cell A maximum power follow-up control unit for instructing the conversion unit to supply a voltage to be charged at a point, a floating voltage command unit for instructing the secondary battery to be a floating voltage, and the comparator. In the mode in which the maximum power follow-up control unit instructs the conversion unit to charge the secondary battery at the maximum power point of the solar cell based on the comparison result in the above, and the floating voltage command unit instructs the conversion unit to float. Rechargeable battery with constant voltage Charging devices using a solar cell, characterized in that it comprises a charging mode switching unit automatically switches to a mode for charging. 5. The charging device using a solar cell according to claim 3, wherein the floating voltage is set to a voltage that complements the self-discharge of the secondary battery.