JP3214201B2 - Backflow prevention device and solar cell protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow prevention device and a solar cell protection device.

[0002]

2. Description of the Related Art Normally, when photovoltaic power is generated, a solar cell that converts light energy into electric energy is used as a power source, and the power generated there is supplied to a load. Further, a storage battery is connected in parallel with the load, and during the daytime, solar power is generated and the storage battery is charged while storing power while supplying power to the load. By the way, when the amount of sunlight in the morning and evening is small or when there is no amount of sunlight in the night, the output voltage of the solar cell group becomes lower than the terminal voltage of the storage battery. Then, since the charging process cannot be performed, power is supplied to the load using the power stored in the storage battery.At this time, in order to prevent the current flowing out of the storage battery from flowing into the solar cell, A diode for preventing backflow is connected in series between the battery and the storage battery to protect the solar battery and to supply the electrical energy of the storage battery to the load side.

However, in the above-described conventional apparatus, when power is supplied from a solar cell during daytime when solar power is generated,
Since the current flowing from the solar cell always passes through the diode, an energy loss due to a voltage drop (0.5 V) in the diode always occurs, which causes a reduction in power generation efficiency.

[0004] In addition, the diode is used as a backflow preventing element in various electric circuits because it has no mechanical deterioration without being limited to the above-described solar cell protection device. For a reason, when a current flows in the forward direction, a power loss of a value obtained by multiplying the current by the voltage drop always occurs, and the influence of the loss increases with a recent decrease in voltage. There is a problem that.

[0005] In order to solve such a problem, for example, there is a DC power supply device disclosed in Japanese Patent Application Laid-Open No. 2-168819. The present invention provides a relay switch having a normally closed contact in parallel with the backflow prevention diode, closes the contact at normal times when current is flowing in the forward direction, short-circuits both ends of the backflow prevention diode, and bypasses the backflow prevention diode. In this case, unnecessary power consumption is suppressed.

When a current is to flow in the reverse direction, the coil constituting the relay is energized to open a contact, and a reverse current preventing diode suppresses the reverse current. Focusing on the fact that such a reverse current state is caused by a power failure or momentary power failure of the primary side power supply, monitoring the output voltage of the primary side power supply, and energizing the coil when detecting a decrease in the output voltage. I have to.

[0007]

However, in the above-described conventional apparatus, the backflow preventing function cannot be sufficiently exerted for the following reasons. That is, since it is detected that the voltage drops, it is difficult to accurately detect the reverse current state of the current, and there is a possibility that an error may occur. When this conventional device is mounted on a solar power generation system to prevent backflow from a storage battery to a solar battery, the output voltage of the solar battery becomes almost constant regardless of brightness, and thus the voltage drop is reduced. Is extremely difficult to detect.

Further, in order to open a contact at the time of a momentary power failure or power failure,
Since power is supplied to the coil through the instantaneous interruption detection circuit and the diode, a new power loss is caused by the diode and the like. In order to prevent the backflow, it is necessary to keep the current flowing through the coil, so that the integrated loss of the diode cannot be ignored. In particular, in the case of a solar cell, the problem of the above-described loss becomes prominent because the time for which the backflow prevention function is exhibited (contacts are opened) is prolonged not only at night but also during the daytime when the amount of sunshine is small.

The present invention has been made in view of the above background, and an object of the present invention is to minimize the loss that occurs when a current flows in the forward direction.
In addition, a backflow prevention device and a solar cell protection device capable of reliably detecting a backflow state, exhibiting a backflow prevention function when desired, and also minimizing power consumption when the backflow is suppressed. Is to provide.

[0010]

In order to achieve the above object, in a backflow prevention device according to the present invention, a coil and a contact which is closed when a current flows through the coil in a certain direction are connected in series. In addition to the connection, a diode is connected in parallel to the contact in the forward direction, and a coil current suppression circuit is provided for suppressing the current flowing through the coil when the current is reversed in the reverse direction. And preferably, the coil current suppression circuit is constituted by a diode connected in parallel and in the opposite direction to the coil. In addition, a coil current suppression circuit can be configured by connecting a series circuit including a capacitor or a diode and an auxiliary coil that generates a magnetic field in a direction opposite to the coil to the coil in parallel. As still another method, an inductance may be connected in series with the coil.

On the other hand, in the solar cell protection device according to the present invention, the backflow prevention circuit is arranged between the solar cell and the storage battery so as to block a current flowing from the storage battery toward the solar cell. It is.

[0012]

For example, when a backflow prevention device is mounted between a solar battery and a storage battery (current flowing from the solar battery to the storage battery is in the forward direction), when the output voltage of the solar battery becomes higher than the battery voltage of the storage battery, the solar battery From the battery flows toward the storage battery. Then, the current flows through the coil, and the contact closes. Then, the current flows to the storage battery through the contact and is charged. At this time, the closed state of the contact is maintained by the current flowing in the coil. Then, there is almost no voltage drop at the contact, and the coil only needs to have enough energy to keep the contact closed, so that the current flowing therethrough is very small. Therefore, there is almost no energy loss occurring in the present device. Also, when the voltage generated from the solar cell falls below the battery voltage of the storage battery, current tends to flow from the storage battery to the solar cell. On the way, the current becomes 0
Alternatively, since the current value becomes a low current value close to 0, the magnetic field generated by the coil is weak, and the holding force required to maintain the contacts in the closed state cannot be obtained. Therefore, the contact is opened and the backflow prevention function by the backflow prevention diode operates.

When the current flowing in the forward direction is reversed and suddenly flows in the reverse direction, the current (absolute value) flowing through the coil becomes near 0 for a short time and immediately increases. Then, even if the above-mentioned holding force is reduced due to the mechanical delay of the relay and the contact is about to open, if a large amount of current flows in the opposite direction before the contact is actually opened, the magnetic field generated thereby keeps the contact closed. There is a possibility that. However, in this example, the coil current suppression circuit suppresses sudden fluctuations in the current flowing in the reverse direction and the amount of the fluctuation. I do.

Further, at the moment when the contact is closed, the resistance value of the backflow prevention circuit is reduced, so that the current value is increased, so that the contact is more firmly closed. Conversely, the current value is decreased, and the contact cannot be held. In this case, the contact is opened, but at this time, the resistance value of the backflow prevention circuit increases, so that the current value decreases and the electromagnetic force further decreases. Therefore, chattering of the contact does not occur.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a backflow prevention device and a solar cell protection device according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a first embodiment of the present invention. This example shows an example in which the backflow prevention device is used as a solar cell protection device. As shown in FIG. 1, a storage battery 2 and a load 3 are connected in parallel to a solar cell 1, and the power generated by the solar cell 1 is supplied to the storage battery 2 to be charged and to the load 3. Further, in this example, the switching element 4 is connected between both terminals of the solar cell 1 so that the terminals can be short-circuited at a predetermined timing. More specifically, when the storage battery 2 is fully charged, the short-circuit control circuit (not shown) detects that the storage battery 2 is fully charged, turns on the switching element 4 to make it conductive, and cuts off the power supply from the solar cell 1. Is suppressed from being overcharged. Then, a backflow prevention device (protection device) 5 according to the present invention is arranged in series between the solar cell 1 and the storage battery 2. In addition, the storage battery 2 has an internal resistance, and its resistance value is, for example, about 0.18Ω.

Here, the backflow prevention device 5 has a backflow prevention diode 6 and a contact (normally open) 7 is connected in parallel between both terminals of the backflow prevention diode 6. A coil 8 is arranged in series with a parallel circuit formed by the backflow prevention diode 6 and the contact 7. The coil 8 is formed using a winding having a very small resistance value, for example, 0.002Ω. The contact 7 is closed when a predetermined amount of current flows through the coil 8. That is, the contact 7 and the coil 8 constitute a current relay. The rating of the backflow prevention diode 6 is 1.0 V in this example.

Further, a diode 10 as a coil current suppressing circuit is provided in parallel with and in the opposite direction to the coil 8. Accordingly, when a forward current flows in the entire system (current flows from the solar cell 1 to the storage battery 2 and the load 3), the current flows in the coil 8 without flowing because the diode 10 is in the reverse direction. That is, in such a case, the backflow prevention device 5 is equivalent to a device in which the diode 10 is not provided. On the other hand, when a reverse current flows in the entire system, a current also flows in the diode 10, but a voltage between terminals at both ends thereof, that is, a voltage applied to the coil 8 is -0.5V. In this example,
Although the rating of the diode 10 is made smaller than that of the reverse charge prevention diode, the present invention is not necessarily required to be made smaller, and may be the same or conversely larger. However, it is preferable to reduce the rating of the diode 10 because the voltage applied to the coil 8 at the time of backflow can be suppressed and the contact can be surely closed.

The characteristics of this current relay are such that when the rated current is 10 A, the contact 7 closes when the current flowing through the coil 8 is about 7 A, and once closed, the contact 7 opens when the current drops to about 1 A. Has the following hysteresis characteristics. Therefore, as shown in FIG. 2A, if the current continues to flow through the backflow prevention diode, the energy loss with respect to the current value is proportional to the current value. Similarly, the loss caused by the coil 8 with respect to the current value is proportional to the square of the current, and thus has a characteristic shown by a broken line (contact closed) in FIG.
Than ² R). However, as is apparent from the figure, since the resistance value of the coil 8 is originally very small, it is extremely small as compared with the loss of the diode. The total loss of the backflow prevention device is the sum of the loss in the diode 6 and the loss in the coil 8.

Therefore, until the contact 7 closes 7A, the loss is the sum of the two. However, when the contact 7 closes and the contact 7 closes, the loss is almost completely due to the coil 8 and becomes very small. At the moment when the contact is closed, the resistance value of the backflow prevention circuit is reduced, so that the current value is increased as shown by the arrow in the figure, and a force is exerted in a direction to close the contact more firmly. In this example, since the current relay has hysteresis, once the contact 7 is closed, even if the current value decreases and becomes 7 A or less, the contact does not open immediately. The contacts open only when: Therefore, until then, there is basically only the loss in the coil 8.

Also, when the contact 7 is opened at 1 A or less,
Since the current flows through the backflow prevention diode 6, the resistance value of the backflow prevention circuit also increases and the current value decreases as indicated by the arrow in the drawing, so that a force acts in the direction in which the contacts open more. Therefore, the occurrence of chattering is suppressed due to the change in the resistance value that occurs when the contact is opened and closed. In addition, in the present embodiment, the effect is more remarkable because the hysteresis is provided. The same can be said for the case where the storage battery 2 is almost fully charged and the amount of current flowing from the solar cell 1 is decreasing.

If the sunshine of one day increases or decreases at noon as shown in FIG. 3B, the power generation (current value) of the solar cell 1 due to the increase or decrease is indicated by a broken line in FIG. , But when it is approximated to a triangle for simplification of calculation, it is shown by a solid line. Therefore, in the case of only the conventional diode, the current always flows through the diode, causing a loss, and thus there was an energy loss of 50 Wh (indicated by hatching in FIG. (D)). Although the loss is slightly larger than that of the diode alone, it is almost eliminated thereafter, so that the loss is almost as shown by the hatched portion in FIG.
7Wh. Further, by reducing the current value at which the contacts close, the loss can be further reduced.

In this embodiment, the value of the current flowing through the backflow prevention diode is smaller than the rated value (7 in the above example).
0%), it is possible to use a smaller capacity (smaller and less expensive) than the conventional one, and as a result, it is possible to suppress the amount of heat generated by the diode and to eliminate or reduce the heat radiation means. It also has ancillary effects such as being able to do so.

Next, consider a case where the direction in which the current flows suddenly reverses. As shown in FIG. 2, in a normal case, when the current becomes zero, the holding force is reduced and the contact is opened as described above, but as shown by a broken line in FIG. The current value (absolute value) flowing through the coil 8 increases before the opening of the contact 7, and the reverse current causes a holding force to the contact 7, and the contact 7 remains closed (both ends of the backflow prevention diode 6 are short-circuited). ), And the backflow prevention function may not be exhibited. However, in this example, the change in current is slowed down by the diode 10 and the voltage applied to the coil 8 is -0.5 V
, The current change is slow and the amount of change is small as shown by the solid line in FIG. Therefore, the contact 7 is reliably opened. Once opened, the reverse current is interrupted by the backflow prevention diode 6, so that no current flows to the coil 8, and the contact 7 remains open.

FIG. 4 shows a second embodiment of the present invention.
As shown in the drawing, in this example, a coil current suppression circuit including a capacitor 11 and an auxiliary coil 12 connected in series is provided in place of the diode 10. The magnetic field generated from the auxiliary coil 12 is adjusted so that a force acts in a direction opposite to the magnetic field generated by the coil 8, that is, in a direction to open the contact 7.

In the case where the current suddenly changes from positive to negative at the time of reverse flow, a current flows through the auxiliary coil 12 via the capacitor 11 and the magnetic field generated by the current causes the magnetic field generated by the coil 8 to change. The force for canceling and closing the contact 7 was instantaneously reduced to ensure that the contact 7 was disconnected. That is, as shown in FIG. 5, if the magnetic flux generated by the current flowing through the coil 8 at the time of reverse flow is as shown by a broken line in the figure, the magnetic flux actually applied to the contact 7 is the magnetic flux generated by the auxiliary coil 12. It decreases by the amount and becomes smaller as shown by the solid line in FIG. Thereby, the contact 7 is reliably opened. The strength of the magnetic field generated by the coil 8 and the strength of the magnetic field generated by the auxiliary coil 12 are not necessarily required to be equal. In a normal stable state (a constant current flows in the forward direction), the DC component is insulated by the capacitor 11 and the auxiliary coil 1
2 is not energized. In addition, the other configuration and operation and effect are the same as those of the above-described embodiment, and the description thereof will be omitted.

FIG. 6 shows a third embodiment of the present invention.
In this embodiment, the operation principle and the like are almost the same as those of the above-described second embodiment (combination of the first embodiment and the second embodiment).
Thus, a diode 15 is provided in place of the capacitor 11,
The diode 15 is turned in the reverse direction (direction in which the reverse current flows)
Set to.

With this configuration, when a current is flowing in the forward direction, the auxiliary coil 1 is
2, the current flows through the auxiliary coil 12 in the opposite direction to the above, and the contact 7 is reliably opened. Note that the diode 15 in this example is
Exhibits the same function as the diode 10 in the first embodiment. Note that the other configuration, operation, and effect are the same as those of the above-described embodiment, and thus the description thereof is omitted.

FIG. 7 shows a fourth embodiment of the present invention.
In this embodiment, unlike the above embodiments, an inductance 16 is provided in series with the coil 8. This slows down the current change, and even if a sudden current change from positive to negative occurs at the time of backflow, the degree of the change is caused by the inductance 16 (formed by winding the toroidal core in this example). Was reduced to ensure that the contacts were opened.

That is, as shown by the broken line in FIG. 8, even if there is a sudden current change due to the reversal of the direction in which the current flows, the provision of the inductance 16
The current actually flowing through the coil 8 changes gradually as shown by the solid line in FIG. Note that the other configuration, operation, and effect are the same as those of the above-described embodiment, and thus the description thereof is omitted.

In each of the above-described embodiments, the opening and closing of the contacts is controlled based on the direction and magnitude of the current flow, so that the present invention can be applied irrespective of the terminal voltage (rating) of the solar cell or storage battery. High versatility.

Further, in each of the above-described embodiments, an example was described in which each was used as a protection device for a solar cell. However, the present invention is not limited to this and can be used as various backflow prevention devices. Of course. Further, even in the case of mounting on a photovoltaic power generation system, it goes without saying that the present invention is not limited to the configuration of each of the above-described embodiments (where a short-circuiting switching element is installed), but can be mounted on various systems.

[0032]

As described above, in the backflow prevention device and the solar cell protection device according to the present invention, since the relay having almost no voltage drop is used, the energy loss caused by the forward flowing current is suppressed as much as possible. You. In addition, a reverse current prevention diode and a contact are connected in parallel, and a coil is connected in series with the parallel circuit so that a forward current flows through the coil to close the contact. The diode prevents backflow without power loss. Therefore, the total energy loss can be reduced as much as possible even when viewing the entire operation. Further, occurrence of chattering at the contact can be suppressed. In addition, even in the case where the reverse current suddenly occurs and the current value of the reverse current increases, the coil current suppressing circuit suppresses the rapid fluctuation and the fluctuation width. Even if there is a mechanical delay of the relay, the contact can be reliably opened at the time of backflow.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation principle of the first embodiment.

FIG. 3 is a diagram illustrating an operation principle of the first embodiment.

FIG. 4 is a diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing the operation principle of the second embodiment.

FIG. 6 is a diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram showing a fourth embodiment of the present invention.

FIG. 8 is a diagram showing the operation principle of the fourth embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 solar cell 2 storage battery 5 backflow prevention device 6 backflow prevention diode 7 contact 8 coil 10 diode (coil current suppression circuit) 11 capacitor (coil current suppression circuit) 12 auxiliary coil (coil current suppression circuit) 15 diode (coil current suppression circuit) 16 Inductance (Coil current suppression circuit)

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J ^7/ 00-7/12 H02J ⁷ /34-7/36

Claims (5)

(57) [Claims] 1. A coil and a contact that is closed when a current flows through the coil in a certain direction are connected in series, a diode is connected in parallel to the contact in a forward direction, and the current flows in a reverse direction. A backflow prevention device comprising a coil current suppression circuit for suppressing a current flowing through the coil when the current is reversed. 2. The backflow prevention device according to claim 1, wherein the coil current suppression circuit includes a diode connected to the coil in parallel and in a reverse direction. 3. The coil current suppressing circuit is connected in parallel to the coil in a series circuit including a capacitor or a diode and an auxiliary coil for generating a magnetic field in a direction opposite to a magnetic field generated by the coil at the contact. The backflow prevention device according to claim 1, wherein the backflow prevention device is configured by: 4. The backflow prevention device according to claim 1, wherein the coil current suppression circuit comprises an inductance connected in series with the coil. 5. A backflow prevention circuit according to claim 1, which is arranged between a solar cell and a storage battery;
A solar cell protection device configured to block a current flowing from the storage battery toward the solar cell.