JP3267054B2 - Power storage device for solar power - 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 storage device for power generated by a solar cell, and more particularly to a power storage device for power generated by a solar cell, which efficiently charges the power generated by the solar cell.

[0002]

2. Description of the Related Art A solar cell is a device that directly converts light energy into electric energy. As shown in a voltage-current (VI) characteristic diagram of FIG. And the generated voltage increases.

As can be seen from FIG. 8, in a solar cell, when the light intensity is constant, the generated current value is almost constant while the generated voltage V is small, and when the generated voltage V exceeds a predetermined value. There is a characteristic that the generated current decreases. Therefore, there is a predetermined voltage Vp at which the electric power, which is the product of the generated voltage and the generated current, is maximized. This is shown in FIG.
In order to efficiently store the power generated by the solar cell in the storage battery, it is necessary to perform a power storage operation at a point where the power becomes maximum.

On the other hand, the electric power generated from the solar cell varies depending on the light intensity as described above and also varies depending on the temperature of the solar cell. FIG. 10 shows the temperature T of the solar cell.
And the optimum voltage Vp at which the generated power is maximized.

As described above, since the above-described Vp varies depending on the operating conditions of the solar cell, control has been conventionally performed so that the power storage operation can always be performed at the maximum point of the power generated by the solar cell. For example, Japanese Patent Application Laid-Open No. 3-253234 discloses that a DC / DC converter is connected in series between a solar battery and a storage battery, and a voltage on an input side and an output side of the DC / DC converter, a current on an output side, and A photovoltaic power generation device that controls an output voltage of a DC / DC converter from a determined reference voltage is disclosed.

FIGS. 11 and 1 show still another example of a control method.
As shown in FIG.

The example shown in FIG. 11 utilizes the characteristics of the solar cell shown in FIG. That is, the characteristic relationship of FIG. 10 is stored in the memory 50, the optimum voltage Vp is calculated from the memory 50 based on the temperature T of the solar cell, and the generated voltage V of the solar cell is subtracted from the optimum voltage Vp. Subtract with. The output of the subtractor 52 is the integrator 5
4. The signal is converted into a pulse width modulated control signal via a pulse width modulation (PWM) circuit 56 and output. The control signal controls the generated voltage V to be equal to the optimum voltage Vp.

In the example shown in FIG. 12, the analog signals of the generated voltage V and the generated current I of the solar cell are A / A.
The digital signal is converted by the D converter 58 into a digital signal.
The voltage output and the current output of the / D converter 58 are multiplied by the multiplier 6
Multiplied by zero. The output of the multiplier 60 is input to the maximum value control circuit 62, and a control output such that the output of the multiplier 60 becomes the maximum value is output from the maximum value control circuit 62. The digital signal output from the maximum value control circuit 62 is D / A
The signal is converted into an analog signal by the
The signal is output as a pulse width modulated control signal via the circuit 66, and the control signal is controlled so that the output of the multiplier 60 becomes the maximum value.

The multiplier 60 and the maximum value control circuit 6
2. The D / A converter 64 is a microcomputer 68
It is composed of

[0010]

However, the conventional devices configured as described above have the following problems.

First, the conventional example described in Japanese Patent Application Laid-Open No. 3-253234 has a complicated circuit configuration because there are a plurality of voltages and currents to be detected and a means for generating a reference voltage. There was a problem that the cost was increased.

Further, the conventional example shown in FIG. 11 can be constituted by an analog circuit and the circuit constitution can be relatively simplified.
There is a problem that the error of the memory 50 is large and a problem that it is not possible to absorb variations in the temperature characteristics of the battery caused by variations in the sensor mounting location and variations between batteries.

Further, the conventional example shown in FIG.
Since the converter 58, the microcomputer 68, and the like are used, in addition to the problem that the circuit configuration is complicated, the cost is large, and the shape is large, the current consumption is large, and the power consumption is larger than the power generation amount under a certain light or less. There was a problem that the meaning of use was lost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to efficiently generate electric power from a solar cell with a simple configuration without using an expensive circuit such as a microcomputer. An object of the present invention is to provide a power storage device of solar cell generated power that can store power. Another object is to provide a solar cell including such a power storage device.

[0015]

In order to achieve the above object, an invention according to claim 1 of the present application is a power storage device for a solar cell generated electric power, and a transformer for changing a voltage generated by the solar cell. And current control means for detecting a charging current of a storage battery that stores power output from the voltage transforming means, and control means for controlling the voltage transforming means such that the current detected by the current detecting means is maximized. Equipped , said control
The means includes a dither for generating a periodic signal oscillating at a predetermined cycle.
Circuit and a maximum of a periodic signal generated from the dither circuit.
At the timing of the current value and the minimum value
A pair of samples that sample and hold the current detection value
The output of the pull-hold circuit and the output of each sample-hold circuit
A comparator for comparing forces and integrating the output signal of the comparator.
An integrator, an output signal of the integrator and the dither circuit
An adder for adding the periodic signal generated from the adder;
The output signal of the transformer is pulse width modulated to control the transformer.
And a modulation circuit for generating a control signal for the
A comparator is provided at the timing of the maximum value of the periodic signal.
The current detection value is at the timing of the minimum value of the periodic signal.
If the current value is larger than the current detection value in
Signal to increase output and decrease if small
Is output .

[0016]

The invention according to claim 2 of the present application is characterized by including the power storage device of the power generated by the solar cell according to claim 1 .

[0018]

Therefore, according to the first aspect of the present invention, only the charging current of the storage battery is detected and the charging current becomes the maximum value in order to charge the storage battery with the power generated from the solar cell most efficiently. Since such control is performed, the circuit configuration is simplified and the device can be downsized. All circuits are analog
By using circuits, expensive circuits such as microcomputers can be used.
It is not necessary to use it, and if high reliability can be obtained at low cost
In both cases, the equipment can be downsized and current consumption can be kept low.
Can be.

[0019]

According to the second aspect of the present invention, the solar cell and the power storage device for the power generated by the solar cell can be integrated.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a basic configuration of a power storage device for solar cell power generation according to this embodiment. A choke coil 14, a diode 16, capacitors 18, 20 and a switch 22 are provided between the solar cell 10 and the storage battery 12.
Is connected. In the transformer 23, the choke coil 14 and the switch 22 are combined, and the transformer 22 performs a transformer operation by opening and closing the switch 22.
To be removed. Further, when the output voltage of the storage battery 12 and the output voltage of the transformer 23 are reversed, a diode 16 is used to prevent the current from flowing back from the storage battery 12.
Note that a so-called step-up type is used as the transformer 23 of the present embodiment, but a step-down type can also be used.

The switch 22 is constituted by a switching element such as a bipolar transistor and an FET. This switch 22 is connected to a control circuit 2 which is a control means of the present invention.
4 is controlled by a control signal Sc. The control circuit 24 generates a control signal Sc based on the charging current Ib of the storage battery 12, and the charging current Ib is detected by measuring a current flowing through the shunt resistor 26 by a voltmeter 28 as current detecting means.

Next, the operation of the circuit shown in FIG. 1 will be described.

As described in the above-mentioned conventional example, in order to efficiently charge the electric power generated by the solar cell 10 to the storage battery 12, it is necessary to perform a charging operation at a point where the electric power generated by the solar cell 10 is maximized. There is. The generated voltage of the solar cell 10 is Vc, the generated current is Ic, and the charging voltage of the storage battery 12 is Vc.
As b, since the charging current is Ib as described above, the generated power P of the solar cell 10 is as follows: P = Vc × Ic = Vb × Ib (1) Here, since the charging voltage Vb of the storage battery 12 is generally constant during the charging operation, the point at which the generated power P of the solar cell 10 becomes maximum is substantially equal to the point at which the charging current Ib becomes maximum. At this point, the power generation voltage Vc of the solar cell 10 matches Vp shown in FIG.

Therefore, in this embodiment, the voltmeter 28
The control circuit 24 controls the opening and closing of the switch 22 of the transforming means 23 so that the charging current Ib measured by the above becomes maximum. Thereby, the power generated by the solar cell 10 can be charged efficiently.

In FIG. 1, the value of the charging current of the storage battery 12 is input from the current measuring voltmeter 28 to the control circuit 24,
A control signal Sc is output from the control circuit 24, and the ratio of the time between opening and closing of the switch 22 is determined by the control signal Sc. In the transformer 23, the ratio of the input and output voltages is determined by the ratio of the time of opening and closing of the switch 22.

On the other hand, as described above, since the charging voltage Vb of the storage battery 12 is constant during the charging operation, the power generation voltage Vc and the power generation current Ic of the solar cell 10 are changed by the operation of the switch 22, and the charging current Ib is controlled to the maximum. You. More specifically, the ratio of the opening and closing times of the switch 22 is controlled so that the generated voltage Vc matches the above Vp.

According to the above configuration, since the control can be performed without depending on the charging voltage Vb of the storage battery 10, the voltage of the solar cell 10 can be freely selected. Further, if the switch 22 is opened, the circuit can be used as a through circuit without switching the circuit, so that the reliability is increased simply.

FIG. 2 is a block diagram showing the configuration of the control circuit 24 described above. In FIG. 2, the charging current Ib is
The sample is held by the two sample and hold circuits 30 and 32. The timing of this sample hold is determined by the dither circuit 34. That is, the dither circuit 34 generates a periodic signal that oscillates at a predetermined cycle.
For example, in this embodiment, a triangular wave signal is used. The above-described sample hold is performed at the timing of the maximum value and the minimum value of this signal. In FIG. 2, the timing of the maximum value is indicated by A, and the timing of the minimum value is indicated by B. The charging current Ib at the timing A of the maximum value in the sample and hold circuit 30 and the timing B of the minimum value in the sample and hold circuit 32. Are sampled and held, respectively.

The charging current Ib sampled and held by the sample and hold circuits 30 and 32 is compared by the comparator 36, and the hold value of the sample and hold circuit 32 is subtracted from the hold value of the sample and hold circuit 30. Also,
The output of the comparator 36 is integrated by an integrator 38. That is, in this embodiment, PI control is used.

The output of the integrator 38 is added by the adder 40 to the output signal of the dither circuit 34, that is, the triangular wave signal. The output of the adder 40 is input to the inverting terminal of the comparator 42. Further, a triangular wave signal is input to the non-inverting terminal of the comparator 42 from the triangular wave signal transmitter 44, and a pulse signal whose pulse width is modulated by the magnitude of the output of the adder 40 is output from the comparator 42. This pulse signal becomes the control signal Sc for the switch 22. In this case, when the output of the adder 40 is higher than the triangular wave signal, the pulse signal is at a high level, and when the output is opposite, the pulse signal is at a low level. Therefore, the duty ratio of the pulse signal is determined by the level of the output of the adder 40. Here, the comparator 42 and the triangular wave signal transmitter 44 constitute a modulation circuit of the present invention.

Next, the operation of the control circuit 24 and the control method of the transformer 23 will be described.

As described above, the opening and closing of the switch 22 is controlled by the pulse signal output from the comparator 42.
In the present embodiment, the switch 22 is configured to be closed when the pulse signal is at a high level and to be opened when the pulse signal is at a low level. As a result, when the output of the adder 40 becomes high, the high level time of the pulse signal becomes short.
2 is also shortened, and the power generation voltage Vc of the solar cell 10 is increased. Conversely, when the output of the adder 40 decreases, the time during which the switch 22 is closed increases, and the power generation voltage Vc also decreases.

Since the output signal of the dither circuit 34 is added to the output of the integrator 38 in the adder 40, the output oscillates at the same cycle as the output signal of the dither circuit 34. Therefore, the duty ratio of the pulse signal, which is the control signal Sc, also oscillates, and the power generation voltage Vc of the solar cell 10 oscillates in the same cycle. As a result, the charging current I
b also oscillates in the same cycle as the output signal of the dither circuit 34. This is shown in FIG.

On the other hand, the comparator 36 subtracts the sample-and-hold value of the sample-and-hold circuit 32 from the sample-and-hold value of the sample-and-hold circuit 30, so that the charging current Ib at the timing A of the maximum value of the output signal of the dither circuit 34 is obtained. The sign of the output signal is determined by the magnitude of the charging current Ib at the timing B of the minimum value. That is, the output of the comparator 36 indicates that the charging current Ib is
It becomes positive when it increases with an increase in the generated voltage Vc of 0, and becomes negative when it decreases.

According to FIG. 9 described above, when the generated voltage Vc is lower than the optimum value Vp, the charging current Ib is reduced to the generated voltage Vc.
When the generated voltage Vc is higher than the optimum value Vp, the charging current Ib decreases as the generated voltage Vc increases. Therefore, the case where the power generation voltage Vc is lower than the optimum value Vp and the case where it is higher than the optimum value Vp will be described separately.

FIG. 4 shows a case where the generated voltage Vc is lower than the optimum value Vp in the relationship between the generated voltage and the generated power shown in FIG. The generated power P increases as the generated voltage Vc increases, and the charging current Ib also increases. Conversely, as the generated voltage Vc decreases, the charging current Ib decreases.

The dither circuit 34 generates a periodic signal as shown in FIG. 5A, which is added to the output of the integrator 38 by the adder 40. As a result, as shown in FIG. 3, the charging current Ib also oscillates in the same cycle. However, since the level of the output of the adder 40 and the level of the generated voltage Vc are the same as described above, the dither circuit 34
The timings A and B of the maximum value and the minimum value of the output signal of FIG. 4 coincide with the maximum and minimum timings of the charging current Ib.
This state is shown in FIG. FIG. 5B shows a case where the charging current Ib is increasing. However, even when the charging current Ib is decreasing, the timings A and B of the maximum value and the minimum value of the output signal of the dither circuit 34 and the charging current are shown. The relationship between Ib maximum and minimum is the same.

In the comparator 36, the charging current Ib at the timing B is subtracted from the charging current Ib at the timing A. As described above, the charging current Ib is at the timing A
At the timing B, the output of the comparator 36 is always positive as shown in FIG. This is not limited to the case where the charging current Ib is increasing as shown in FIG. 5B, and the same result is obtained even when the charging current Ib is decreasing. As a result, the output of the integrator 38 is
It increases as shown in (d).

FIG. 5E shows that the output of the dither circuit 34 is added to the output of the integrator 38 by the adder 40. The output of the adder 40 increases while oscillating at the same cycle as the output signal of the dither circuit 34.

As a result, the generated voltage Vc of the solar cell 10
Also increases while oscillating at the same cycle as the output signal of the dither circuit 34, and increases toward the optimum value Vp. This state is shown in FIG. At this time, since the generated voltage Vc is lower than the optimum value Vp, the charging current Ib also increases while oscillating with the generated voltage Vc and increases toward the maximum value Imax, as shown in FIG. .

Next, of the relationship between the generated voltage and the generated power shown in FIG. 9, the case where the generated voltage Vc is higher than the optimum value Vp will be described. FIG. 6 illustrates this case.
The generated power P decreases as the generated voltage Vc increases, and the charging current Ib also decreases. Conversely, the charging current Ib increases as the generated voltage Vc decreases.

FIG. 7A shows an output signal of the same dither circuit 34 as in FIG. 5A, and FIG. 7B shows a charging current Ib oscillating at the same cycle as the output signal. However, FIG. 7B is different from FIG. 5B in that the charging current Ib is minimized at the timing A of the maximum value of the output signal of the dither circuit 34 and is maximized at the timing B of the minimum value. It is. In FIG. 7B, the charging current Ib
FIG. 5B shows a case in which is increasing, but the same applies to a case in which it is decreasing.

As a result, in the comparator 36, the charging current Ib
The maximum value is subtracted from the minimum value of
Is always negative as shown in FIG. 7 (c). Therefore, the result is opposite to that of FIG.

Since the output of the comparator 36 is integrated by the integrator 38, as shown in FIG.
Output decreases.

The output of the dither circuit 34 is added to the output of the integrator 38 by the adder 40, as shown in FIG.
It is shown in (e). The output of adder 40 is a dither circuit 34
And decreases while oscillating at the same cycle as the output signal.

As a result, the generated voltage Vc of the solar cell 10
Also decreases while oscillating at the same cycle as the output signal of the dither circuit 34, and decreases toward the optimum value Vp. This is shown in FIG. At this time, since the generated voltage Vc is higher than the optimum value Vp, the charging current Ib increases while oscillating with the generated voltage Vc and increases toward the maximum value Imax, as shown in FIG. .

As described above, regardless of whether the generated voltage Vc is lower or higher than the optimum value Vp, the control method of this embodiment controls the generated voltage Vc to always approach the optimum value Vp, and the charging current Ib Also converge to the maximum value Imax. This is shown in FIG. Note that, as shown in FIG. 9, the power generation voltage Vc near the optimum value Vp.
Does not change much. As a result, as shown in FIG. 3, when the charging current Ib approaches Imax, its amplitude decreases.

In the embodiment described above, since the devices are all constituted by analog, the size of the device can be reduced. For this reason, each cell of the solar cell 10 can be provided with one power storage device. In this manner, optimal control can be performed for each cell of the solar cell 10, and more efficient operation can be performed.

[0051]

As described above, according to the first aspect of the present invention, only the charging current of the storage battery is detected and the control is performed so that this charging current becomes the maximum value. The circuit configuration is simpler than that of the method of reading, and the reliability can be improved and the cost can be reduced. In addition, since all were configured with analog circuits, the microcomputer
It is not necessary to use expensive circuits such as
Reliability is obtained. Furthermore, the device can be downsized and current consumption can be reduced.
This is especially useful when the light is weak.
It is profitable.

[0052]

Further, according to the second aspect of the present invention, the control of the solar cell can be performed finely.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a basic configuration of a power storage device of solar cell generated power according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control circuit of the embodiment of FIG.

3 is an explanatory diagram of control of a storage battery charging current in the embodiment of FIG.

FIG. 4 is a diagram showing the relationship between the generated voltage and the generated power when the generated voltage Vc is lower than an optimum value Vp.

FIG. 5 is an explanatory diagram of a control method according to the present invention.

FIG. 6 is a diagram showing the relationship between the generated voltage and the generated power when the generated voltage Vc is higher than an optimum value Vp.

FIG. 7 is an explanatory diagram of a control method according to the present invention.

FIG. 8 is a voltage-current characteristic diagram of a solar cell.

FIG. 9 is a voltage-power characteristic diagram of a solar cell.

FIG. 10 is a battery temperature-power maximum voltage characteristic diagram of a solar cell.

FIG. 11 is a block diagram showing a conventional power generation voltage control method for a solar cell.

FIG. 12 is a block diagram illustrating a conventional power generation control method for a solar cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Solar cell 12 Storage battery 22 Switch 23 Transformer 24 Control circuit 28 Voltmeter 30, 32 Sample hold circuit 34 Dither circuit 36, 42 Comparator 38 Integrator 40 Adder 44 Triangular wave signal transmitter

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-253451 (JP, A) JP-A-3-18911 (JP, A) JP-A-6-78474 (JP, A) JP-A-56- 91633 (JP, A) Special Table 3-500959 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02J ^7/ 00-7/12 H02J ⁷ /34-7/36 G05F 1/67

Claims (2)

(57) [Claims] 1. A power storage device for generating electric power of a solar cell, comprising: a voltage converting means for changing a voltage generated by the solar cell; and a current detecting means for detecting a charging current of the storage battery for storing electric power output from the voltage converting means. When, and a control means for current detected by said current detecting means to control said transformer means so as to maximize the control means comprises a dither circuit for generating a periodic signal oscillating at a predetermined period, the The maximum value of the periodic signal generated from the dither circuit and
Current detection by the current detection means at the timing of the minimum value
A pair of sample holes that sample and hold the values
And a comparator for comparing the output of each of the sample and hold circuits.
When, an integrator for integrating the output signal of the comparator, is generated the output signal of the integrator from the dither circuit
An adder for adding a periodic signal, and an output signal of the adder, which performs pulse width modulation,
A modulation circuit for generating a control signal for controlling the
And the comparator detects the timing of the maximum value of the periodic signal.
The detected current value is the minimum value of the periodic signal.
If the current is greater than the current detection value in the
Increase the output of the vessel and decrease it if it is small
A power storage device for solar cell generated power, which outputs a signal . 2. A solar cell comprising: a power storage device of the solar cell power generation according to claim 1, wherein.