JPH06283749A - Method and circuit for detecting output of solar cell - Google Patents

Abstract

PURPOSE:To detect the output of a solar cell with high accuracy and facilitate the standardization of a circuit, to get the timing related to the quantity of insolation at sunset, sunrise, or the like, concerning the method and circuit for detecting the output of the solar cell. CONSTITUTION:When detecting the output of a solar battery PV, the output of a solar cell is detected by connecting a semiconductor diode D2 in forward direction to that solar cell PV, and detecting the forward voltage Vf of the semiconductor diode D2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell output detection method and detection circuit. Since the output of the solar cell fluctuates greatly depending on the amount of solar radiation (illuminance) of the sun, it is possible to detect the output of the solar cell and switch the load connection based on the detection result, thereby effectively using the generated power. Has been done.

For example, in a stand-alone type lighting device that can be used by disconnecting it from the system power supply by using a solar cell, the storage battery is charged by the solar cell in the daytime and the lamp is turned on by discharging the storage battery at night. Although it is configured, in order to obtain the timing to turn on the lamp, it is detected that the sunset has occurred based on the output of the solar cell. In such an illuminating device, it is desired to detect the timing of sunset with high accuracy and to effectively use the generated power of the solar cell as much as possible.

[0003]

2. Description of the Related Art FIG. 5 is a circuit diagram of a lighting device 80 according to a conventional output detection method. In FIG. 5, the solar cell PV
Is used as a generator for charging the storage battery BT with the generated power, and an illuminance sensor for detecting a sunset and obtaining a timing for switching from charging the storage battery BT to lighting the lamp LP by the storage battery BT. Is also used as.

That is, the output voltage Vs of the solar cell PV is divided by the two resistors R11 and R12, and when the divided voltage Vd becomes lower than the reference voltage, the comparison control circuit 81 is at sunset. When the signal S1 is detected, a signal S1 is output, the switch element Q1 is turned on by the signal S1, and the lamp LP is turned on.

FIG. 6 is a circuit diagram of a conventional solar power generation system 90 in which various electric loads are operated by electric power generated by a solar cell. In FIG. 6, the resistor R14
When the voltage Vd generated at both ends of the switch becomes higher than the reference voltage, the comparison control circuit 91 turns on the switch SW1, and the power converter 31 operates to supply power to the load 32. Before the switch SW1 is turned on, only the resistors R13 and 14 are connected as the load of the solar cell PV, and the output voltage Vs of the solar cell PV is substantially equal to the open circuit voltage.

In this solar power generation system 90,
Until the generated power of the solar cell PV reaches a certain reference value, the power converter 31 is put into a standby state without being activated, and when it reaches the reference value, it is activated and brought into an operating state for the first time. As a result, the power converter 31 is in the operating state only when the power generated by the solar cell PV is large enough to operate the power converter 31, and the overall operation of the photovoltaic power generation system 90 is stabilized. Has been.

[0007]

However, the conventional detection method as described above has the following problems. First,
The output of the solar cell PV fluctuates according to the amount of solar radiation as described above. That is, FIG. 4 is a diagram showing the relationship between the output voltage Vs and the output current Is of which the solar radiation amount incident on the solar cell PV is a parameter. As shown in FIG. 4, the short-circuit current (= a0, a1, a2 ...) increases in proportion to the amount of solar radiation, and the open-circuit voltage (= b0, b1, b2 ...) Gently increases as the amount of solar radiation increases, and the maximum output (= Pm
ax0, Pmax1, Pmax2 ...) Increases almost in proportion to the amount of solar radiation. That is, the short-circuit current and the maximum output both greatly vary depending on the amount of solar radiation, but the open-circuit voltage does not vary significantly.

Therefore, in the photovoltaic power generation system 90 shown in FIG. 6, the amount of change in the detected voltage Vd is small, which lowers the detection accuracy and allows the power converter 31 to be activated at an appropriate timing. No, solar cell P
The generated power of V may not be effectively used or the operation of the solar power generation system 90 may become unstable.

In the lighting device 80 shown in FIG. 5, since the terminal voltage Vb of the storage battery BT during charging is small, the output voltage Vs of the solar cell PV at that time is also small. Therefore, the amount of change in the voltage Vd detected in the vicinity of the time of sunset becomes small, which decreases the detection accuracy, and the lamp LP is lit up even though there is still time until sunset, or the lamp LP remains Occasionally, it would not turn on.

Further, in the lighting device 80 shown in FIG.
The output voltage Vs of the solar cell PV is the voltage Vb of the storage battery BT.
Is the sum of the forward voltage Vf of the diode D1 and is represented by the following equation (1).

Vs = Vb + Vf (1) Therefore, the output voltage Vs of the solar cell PV is different due to the difference in the type of the storage battery BT, for example, the nominal voltage, the capacity, the state of the storage battery, etc., and is detected accordingly. The voltage Vd that occurs will also have different values. Therefore, the values of the resistors R11 and R12 have to be redesigned according to the type of the storage battery BT used in the lighting device 80, and it is not easy to standardize the detection circuit.

In view of the above-mentioned problems, the present invention can detect the output of the solar cell with high accuracy in obtaining the timing related to the illuminance such as at the time of sunset or sunrise and the circuit. It is an object of the present invention to provide a solar cell output detection method and a detection circuit capable of easily standardizing the above.

[0013]

In order to solve the above-mentioned problems, the method according to the invention of claim 1 detects a solar cell output by connecting a semiconductor diode to the solar cell in a forward direction. This is a method for detecting the output of a solar cell, which detects the forward voltage of a semiconductor diode.

According to a second aspect of the present invention, the semiconductor diode is connected between the negative electrode of the solar cell and a ground line, and the potential on the cathode side of the semiconductor diode is amplified by an inverting amplifier to detect a detection signal. Is a method of detecting the output of the solar cell.

A circuit according to a third aspect of the present invention is a semiconductor diode connected in a forward direction between a negative electrode of a solar cell and a ground line, and an inverting amplifier for inverting and amplifying a potential on the cathode side of the semiconductor diode. And are configured.

[0016]

The solar cell output current flows through the semiconductor diode, which causes a forward voltage across the semiconductor diode. The generated forward voltage is inverted and amplified by, for example, an inverting amplifier and output as a detection signal. The detection signal is compared with an appropriate reference voltage by, for example, a comparator, and the load is controlled based on the comparison result.

Since there is a strong positive correlation between the output current of the solar cell and the amount of solar radiation and the generated power, the forward voltage is detected to correlate with the illuminance (insolation) such as at sunset or sunrise. The timing to do is obtained.

[0018]

1 is a circuit diagram of an illuminating device 1 using a detection circuit 12 according to the present invention. In FIG. 1, components having the same functions as those of the components shown in FIG. 5 are designated by the same reference numerals, and description thereof will be omitted or simplified.

In FIG. 1, a lighting device 1 includes a solar cell P.
V, a storage battery BT, a backflow prevention diode D1, a lamp LP, a switch element Q1, a comparison control circuit 11, and a detection circuit 12.

The detection circuit 12 includes a detection diode D2.
And an inverting amplifier 21 and the like. The diode D2 for detection is for detecting the output current Is of the solar cell PV, and is forward between the negative electrode of the solar cell PV and the ground line (GND) as a part of the load of the solar cell PV. It is connected to the.

The inverting amplifier 21 is composed of an operational amplifier OP operated by a single power source and resistors R1, R2, R3, etc., and appropriately amplifies the cathode side potential (-Vf) of the detection diode D2. The output voltage Vout is output to the comparison control circuit 11 after being inverted and amplified at a rate.

The comparison control circuit 11 receives the input voltage Vo.
ut and a reference voltage Vr (not shown) are compared, and the voltage Vo
When ut becomes lower than the reference voltage Vr, the signal S
1 is output to turn on the switch element Q1. When the switch element Q1 is turned on, the lamp LP is turned on by the electric power supplied from the storage battery BT.

Now, while the storage battery BT is being charged by the solar cell PV, a current Is flows through the charging circuit. This current Is produces a forward voltage Vf across the diode D2.

In general, the forward current I flowing through the diode
f is expressed by the following equation (2). If = Iso [exp (q.Vf / K.T) -1] (2) where, Is: reverse saturation current K: Boltzmann's constant T: absolute temperature q: electron charge From this formula (2), The following equation (3) indicating the forward voltage Vf is obtained.

Vf = (K · T / q) ln (If / Iso + 1) (3) That is, the forward voltage Vf is obtained corresponding to the forward current If. The forward current If is the current Is flowing in the charging circuit.
Therefore, the current Is can be detected by detecting the forward voltage Vf.

FIG. 3 is a diagram showing the relationship between the current Is and the voltages Vb, Vs and Vout measured using a circuit equivalent to the lighting device 1. The voltage Vs is the output voltage (operating voltage) of the solar cell PV, and Vb is the terminal voltage of the storage battery BT. A NiCd battery having a nominal voltage of 6 V was used as the storage battery BT, the amplification factor of the inverting amplifier 21 was set to "2", and the switch element Q1 was turned off. Further, the forward voltage V of the diode D1 for backflow prevention and the diode D2 for detection is
It is assumed that f is the same as each other.

As shown in FIG. 3, the output voltage Vs of the solar cell PV is equal to the sum of the voltage Vb of the storage battery BT and the forward voltage (Vf × 2) of the two diodes D1 and D2. The output voltage Vout of the inverting amplifier 21 is twice the forward voltage Vf of the detection diode D2.

Therefore, in the comparison control circuit 11, the output current Is of the solar cell PV can be detected by comparing the voltage Vout with the reference voltage Vr. For example, assuming that the reference voltage Vr is 1.5V, this corresponds to the case where the current Is is 0.25A, and in this case, it is detected whether or not the output current Is of the solar cell PV reaches 0.25A. be able to.

As can be understood from FIG. 4 described in the section of the prior art, since the magnitude of the current Is varies greatly depending on the amount of solar radiation, the detection circuit 12 determines the timing of sunset, the timing of sunrise, etc. The timing related to the amount of solar radiation can be detected with high accuracy.

The state of fluctuation of the current Is is the maximum output P
It is very similar to that of max, and since the current Is and the generated power (power generation amount) have a strong positive correlation, the current I
By detecting s, the electric power generated by the solar cell PV is detected, and various detections for effectively utilizing the electric power generated by the solar cell PV can be easily and accurately performed.

Further, since the current Is is detected by the detection diode D2, even if the nominal voltages of the solar battery PV and the storage battery BT are different, the output of the solar battery PV is stabilized without being affected by it. And can be detected. Therefore, it is not necessary to redesign the constants of the detection circuit as in the conventional case, and it is easy to standardize the detection circuit 12.

Further, since the detection diode D2 is connected between the negative electrode of the solar cell PV and the ground line, it is not necessary to make any changes to the lighting circuit by the storage battery BT and the lamp LP, and the circuit design Is easy. In that case, the cathode side of the diode D2 for detection has a negative potential with respect to the ground line, but since it is inverted to a positive potential by the inverting amplifier 21, subsequent signal processing becomes easy,
The circuit design of the comparison control circuit 11 becomes easy.

FIG. 2 is a circuit diagram of a photovoltaic power generation system 2 using the detection circuit 12 according to the present invention. In FIG.
Components having the same functions as those of the components shown in FIG. 1 or 6 are designated by the same reference numerals, and the description thereof will be omitted or simplified.

The solar power generation system 2 includes a solar cell PV,
The diode D1 for backflow prevention, the switch element Q2, the switch SW1, the power converter 31, the load 32, the comparison control circuit 11a, and the same detection circuit 12 as that used in the lighting device 1 are configured.

In the solar power generation system 2, the inverting amplifier 2
Until the output voltage Vout of 1 reaches the reference voltage Vr, in other words, the generated electric power of the solar cell PV reaches the reference value, it is in a standby state, and when it reaches the reference value, the switch S
W1 is turned on, the power converter 31 is operated, and power is supplied to the load 32.

In the standby state, the comparison control circuit 11a outputs the signal S3 and holds the switch element Q2 in the ON state. In this state, the detection diode D2 is connected in the forward direction as the load of the solar cell PV, and the detection circuit 1
The short circuit current Isc of the solar cell PV is detected by 2. Since the short-circuit current Isc of the solar cell PV greatly changes according to the amount of solar radiation (see FIG. 4), the detection circuit 1
2 makes it possible to detect with high accuracy the timing related to the amount of solar radiation, especially the timing when the amount of solar radiation is small.

When the voltage Vout reaches the reference voltage Vr,
The comparison control circuit 11a turns off the signal S3 to open the switch element Q2, and turns on the switch SW1 to output the power generated by the solar cell PV to the power converter 31 to put the power converter 31 into an operating state.

In the solar power generation system 2, the detection circuit 12 detects the power generated by the solar cell PV, and when it reaches the reference value, the operation state is entered, so that the power converter 31 is always in a stable state. The load 32 can be operated and a stable electric power can be supplied to the load 32.

In the above embodiment, the circuit configuration of the inverting amplifier 21, the type of elements used, the circuit constants, etc. can be variously changed other than those described above. When there is no risk of backflow from the load side to the solar cell PV, the backflow prevention diode D1 can be omitted. The circuit configuration of the detection circuit 12, the type of elements used, the number of elements, etc.
Various changes can be made along the gist of the present invention. Further, the detection circuit 12 can be applied to various devices or systems other than the lighting device 1 and the solar power generation system 2.

[0040]

According to the present invention, the output of the solar cell can be detected with high accuracy in obtaining the timing related to the illuminance such as at sunset or sunrise, and the standardization of the circuit can be achieved. It can be easily achieved.

According to the second and third aspects of the present invention, it is not necessary to change the load circuit such as the storage battery or the power converter, and the signal output from the detection circuit can be easily processed. Design becomes easy.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an illumination device using a detection circuit according to the present invention.

FIG. 2 is a circuit diagram of a photovoltaic power generation system using a detection circuit according to the present invention.

FIG. 3 is a diagram showing the relationship between current and voltage measured using a circuit equivalent to the lighting device shown in FIG.

FIG. 4 is a diagram showing a relationship between an output voltage and an output current of the solar cell with a solar radiation amount as a parameter.

FIG. 5 is a circuit diagram of a lighting device according to a conventional output detection method.

FIG. 6 is a circuit diagram of a conventional solar power generation system in which various electric loads are operated by electric power generated by a solar cell.

[Explanation of symbols]

 12 detection circuit (output detection circuit) 21 inverting amplifier PV solar cell D2 detection diode (semiconductor diode)

Claims (3)

[Claims] 1. A method for detecting an output of a solar cell, which comprises detecting a forward voltage of the semiconductor diode by connecting a semiconductor diode to the solar cell in a forward direction in detecting the output of the solar cell. 2. The method for detecting output of a solar cell according to claim 1, wherein the semiconductor diode is connected between a negative electrode of the solar cell and a ground line, and a cathode side potential of the semiconductor diode is inverted by an inverting amplifier. A solar cell output detection method that amplifies to obtain a detection signal. 3. A semiconductor diode, which is connected in a forward direction between a negative electrode of a solar cell and a ground line, and an inverting amplifier for inverting and amplifying a cathode side potential of the semiconductor diode. An output detection circuit for a solar cell.