JPH07147738A - Reverse-current protector and solar cell protective device - Google Patents

Abstract

PURPOSE:To provide a reverse-current protector for detecting and eliminating reverse-current, which can suppress an energy loss as low as possible. CONSTITUTION:In a reverse-current protector 5 which is connected between a solar cell 1 and a battery 2 is series, a normally-opened contact 7 is connected to a reverse-blocking diode 6 in parallel and a current coil 8 which performs the switching control of the contact 7 is connected to the diode 6 in series. Further, a diode 10 is connected to the current coil 8 in parallel. The polarity of the diode 10 is such that a reverse current flows. With this constitution, while a current flows from the solar cell 1 to the battery 2 (forward direction), a current is applied to the coil 8 (in which little power is consumed) and the contact 7 is closed and a current flows through the contact 7. When a reverse current appears, the contact 7 is opened and the reverse-current is securely blocked by the reverse-blocking diode 6. Even if the current flow is suddenly changed from the forward direction to the reverse direction, the change is suppressed by the diode 10 and the contact is opened without fail.

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 solar power generation is performed, a solar cell that converts light energy into electric energy is used as a power source, and the electric power generated therein is supplied to a load. Further, a storage battery is connected in parallel with the load, and photovoltaic power generation is performed during the daytime to supply power to the load and charge the storage battery to store power. 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, the power stored in the storage battery is used to supply power to the load.At this time, however, the current flowing out of the storage battery is prevented from flowing into the solar cell side. A diode for preventing backflow is connected in series between the battery and the storage battery to protect the solar cell and to supply the electric energy of the storage battery to the load side.

However, in the above-mentioned conventional device, when power is supplied from the solar cell during the daytime when solar power generation is performed,
Since the current flowing out from the solar cell always passes through the diode, energy loss is always generated due to the voltage drop (0.5 V) in the diode, which is one of the causes of the decrease in power generation efficiency.

Further, the diode is used as a backflow prevention element in various electric circuits because it is not limited to the above-mentioned solar cell protection device and has no mechanical deterioration, but is similar to the above. For that reason, when a current is flowing in the forward direction, there is always a power loss of a value obtained by multiplying the current by the above voltage drop, and the influence of the loss increases with the recent decrease in voltage. I have a problem.

In order to solve such a problem, for example, there is a DC power supply device disclosed in JP-A-2-168819. According to the present invention, a relay switch having a normally closed contact is provided in parallel with a backflow prevention diode, and when the current is normally flowing in the forward direction, the contact is closed to short-circuit both ends of the backflow prevention diode and bypass the backflow prevention diode. This prevents unnecessary power consumption.

When the current is going to flow in the reverse direction, the coil forming the relay is energized to open the contact and the backflow prevention diode suppresses the backflow of the current. Then, paying attention to the fact that such a reverse current state occurs due to a power failure or momentary power failure of the primary power supply, the output voltage of the primary power supply is monitored, and when it is detected that the output voltage has dropped, the coil is energized. I have to.

[0007]

However, in the above-mentioned conventional device, the backflow preventing function cannot be sufficiently exerted for the following reason. That is, since it is detected that the voltage drops, it is difficult to accurately detect the reverse current state of the current, which may cause an error. When the conventional device is mounted on a solar power generation system to prevent backflow from the storage battery to the solar cell, the output voltage of the solar cell becomes almost constant regardless of the brightness, so that the above voltage drops. Is extremely difficult to detect.

Further, in order to open the contact at the time of momentary power failure or power failure,
Since the coil is energized through the instantaneous disconnection detection circuit and the diode, the diode causes a new power loss. Then, in order to prevent the backflow, it is necessary to keep the current flowing through the coil, so the integrated amount of loss in the diode cannot be ignored. In particular, in the case of a solar cell, the problem of the above-mentioned loss becomes remarkable because the time for exhibiting the backflow prevention function (opening the contact) becomes long not only in the nighttime but also in the daytime when the amount of sunlight is small.

The present invention has been made in view of the above background, and an object of the present invention is to reduce the loss generated when a current flows in the forward direction as much as possible.
Moreover, the backflow prevention device and the solar cell protection device can surely detect the backflow state and exert the backflow prevention function at a desired time, and can also suppress the power consumption while suppressing the backflow as much as possible. 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. A coil current suppressing circuit is provided which is connected and a diode is connected in parallel to the contact in the forward direction, and further suppresses the current flowing through the coil when the current is reversed in the reverse direction. And, preferably, the coil current suppressing circuit is composed of a diode connected in parallel and in the reverse direction to the coil. Further, the coil current suppressing 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 that of the coil in parallel to the coil. As 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 the current flowing from the storage battery toward the solar cell. Is.

[0012]

If, for example, a backflow prevention device is installed between the solar cell and the storage battery (the current flowing from the solar cell to the storage battery side is in the forward direction), if the output voltage of the solar cell becomes higher than the battery voltage of the storage cell, the solar cell Current flows from the storage battery to the storage battery side. Then, the current flows through the coil and the contacts close. Then, the above current reaches the storage battery through the contacts and is charged. At this time, the closed state of the contacts is maintained by the current flowing through the coil. Further, there is almost no voltage drop at the contact, and the coil needs only enough energy to keep the contact closed, so that the current flowing therethrough is very small. Therefore, there is almost no energy loss generated in this device. Further, when the voltage generated from the solar cell becomes equal to or lower than the battery voltage of the storage battery, current tends to flow from the storage battery to the solar cell side. The current is 0 on the way
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 necessary to maintain the contact in the closed state cannot be obtained. Therefore, the contact opens, and the backflow prevention function by the backflow prevention diode works.

When the current flowing in the forward direction is reversed and suddenly flows in the opposite direction, the current (absolute value) flowing in the coil becomes near 0 for a short time and immediately increases. Then, even if the holding force decreases due to the mechanical delay of the relay and the contact tries to open, if a large amount of current flows in the opposite direction before it is actually opened, the magnetic field generated by it keeps the contact closed. May occur. However, in this example, the coil current suppression circuit suppresses abrupt fluctuations in the current flowing in the reverse direction and the amount of such fluctuations.Therefore, even if there is mechanical delay in the relay, the contacts will be opened reliably during reverse flow, preventing reverse flow. I do.

In addition, when the resistance value of the backflow prevention circuit decreases at the moment when the contact is closed, the current value rises, and the contact closes more firmly. Conversely, when the current value decreases and the contact cannot be held. The contact opens, but at this time, the resistance value of the backflow prevention circuit increases, so the current value decreases, and the electromagnetic force further decreases. Therefore, contact chattering does not occur.

[0015]

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

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

Further, a diode 10 as a coil current suppressing circuit is installed in parallel with and opposite to the coil 8. As a result, 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 does not flow to the diode 10 because it is in the reverse direction, and the current flows to the coil 8. That is, at this time, the backflow prevention device 5 is equivalent to the device without the diode 10. On the other hand, when a reverse current flows through the entire system, a current also flows through the diode 10, but the voltage across the terminals of the diode 10, that is, the 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 protection diode, the present invention does not necessarily have to be made small, and may be the same or conversely large. However, it is preferable to reduce the rating of the diode 10 because the voltage applied to the coil 8 can be suppressed to a low level during reverse flow, and the contacts can be reliably closed.

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

Therefore, the contact 7 is the sum of the losses until the contact 7 is closed, but when the contact 7 is closed and the contact 7 is closed, the loss is almost due to the coil 8 and becomes very small. The resistance value of the backflow prevention circuit decreases at the moment when this contact is closed, so that the current value increases as indicated by the arrow in the figure, and force acts in a direction to close the contact more firmly. In this example, since the current relay has hysteresis, once the contact 7 is closed, the contact does not immediately open even if the current value decreases to 7 A or less, and in this example 1 A The contact opens only when Therefore, until then, there is basically only the loss in the coil 8.

When the contact 7 is opened below 1 A,
Since the current flows through the backflow prevention diode 6, the resistance value of the backflow prevention circuit rises and the current value decreases, as indicated by the arrow in the figure, so that the force acts more toward the opening of the contact. Therefore, the occurrence of chattering is suppressed due to the phenomenon of resistance value variation that occurs when the contacts are opened and closed, and since hysteresis is provided in this example, the above effect becomes more prominent. The same applies to the case where the storage battery 2 is close to being fully charged and the amount of current flowing from the solar cell 1 is decreasing.

If the sunshine on one day increases or decreases with noon as a boundary as shown in FIG. 7B, the amount of power generation (current value) of the solar cell 1 due to it is shown by a broken line in FIG. In order to simplify the calculation, a solid line is used to approximate the triangle. Therefore, in the case of only the conventional diode, there was an energy loss of 50 Wh because current always flows through the diode to cause a loss (indicated by hatching in Fig. (D)), but in this example, at the beginning of power generation, Although the loss is slightly larger than that of the diode alone, but it disappears after that, so that loss is eventually indicated by the overlapping portion of the hatching in the figure.
Reduced to 7Wh. Further, the loss can be further reduced by lowering the current value for closing the contacts.

In this embodiment, the value of the current flowing in the backflow prevention diode is smaller than the rating (7 in the above example).
Therefore, it is possible to use a capacitor having a smaller capacity (smaller and cheaper) than the conventional one, and as a result, it is possible to suppress the amount of heat generated in the diode, etc. It also has the additional effect of being able to do so.

Next, consider the case where the direction of current flow is suddenly reversed. As shown in FIG. 2, normally, when the current becomes zero, the holding force becomes small and the contact opens as described above. However, as shown by the broken line in FIG. 3, when a large current suddenly flows in the opposite direction, the contact is opened. The current value (absolute value) flowing through the coil 8 increases before the opening of the coil 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). There is a risk that the backflow prevention function will not work. However, in this example, the diode 10 slows down the change in current and the voltage applied to the coil 8 is -0.5V.
Since the limit is set, the current change is slow and the amount of change is small as shown by the solid line in the figure. Therefore, the contact 7 is surely opened. Then, once opened, the reverse current is cut off by the backflow prevention diode 6, so that no current flows to the coil 8, so that the contact 7 maintains the open state.

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

As a result, when the current suddenly changes from positive to negative during reverse flow, the 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 that cancels out and closes the contact 7 is instantaneously reduced so that the contact 7 is reliably released. 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 the 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 small as shown by the solid line in the figure. This ensures that the contact 7 opens. The strength of the magnetic field generated by the coil 8 and the strength of the magnetic field generated by the auxiliary coil 12 do not necessarily have to be the same, and the point is that the contacts can be reliably opened during reverse flow. 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. Further, other configurations and effects are the same as those of the above-mentioned embodiment, and therefore 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 substantially the same as those of the above-mentioned second embodiment (combined the first embodiment and the second embodiment).
Then, a diode 15 is provided instead of the capacitor 11,
Reverse this diode 15 (direction in which reverse current flows)
Set to.

With this configuration, when the current flows in the forward direction, the diode 15 causes the auxiliary coil 1 to operate.
It is possible to suppress the current from flowing to the second coil 2, while the current flows to the auxiliary coil 12 contrary to the above at the time of the reverse current to surely open the contact 7. In addition, the diode 15 in this example
Has the same function as the diode 10 in the first embodiment. Since the other configurations, functions and effects are the same as those of the above-described embodiment, the description thereof will be omitted.

FIG. 7 shows a fourth embodiment of the present invention.
In this embodiment, unlike the above-described embodiments, the inductance 16 is provided in series with the coil 8. As a result, the change in current is blunted, and even if there is a sudden change in current from positive to negative during reverse flow, the degree of change due to the inductance 16 (formed by winding the toroidal core in this example) Was made smaller so that the contacts would open reliably.

That is, as shown by the broken line in FIG. 8, even if there is a rapid current change due to the reversal of the direction of current flow, the provision of the inductance 16 allows
The current actually flowing through the coil 8 changes gently as shown by the solid line in the figure, and the contact 7 can be opened reliably. Since the other configurations, functions and effects are the same as those of the above-described embodiment, the description thereof will be omitted.

In each of the above-mentioned embodiments, since the contact opening / closing control is performed based on the direction and the magnitude of the current flow, it can be applied regardless of the terminal voltage (rating) of the solar cell or the storage battery. , High versatility.

Further, in each of the above-mentioned embodiments, an example in which they are used as a protection device for a solar cell has been described, but the present invention is not limited to this and can be used as various backflow prevention devices. Of course. Further, even when it is mounted on a solar power generation system, it is needless to say that it can be mounted on various systems, not limited to the configuration of each of the above-described embodiments (one in which a switching element for short circuit is installed).

[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 current flowing in the forward direction is suppressed as much as possible. It In addition, since the backflow prevention diode and the contact are connected in parallel, and the coil is connected in series to the parallel circuit and a forward current is applied to the coil to close the contact, the coil is not energized during backflow and the backflow is prevented. The diode can prevent backflow without power loss. Therefore, the total energy loss can be reduced as much as possible even when the entire operation is viewed. Further, chattering of the contact can be suppressed. Moreover, even in the case where the reverse current is suddenly caused and the current value of the reverse current becomes large, the coil current suppressing circuit suppresses the rapid fluctuation and the fluctuation width, so that the coil and the contact are temporarily configured. Even if there is a mechanical delay in the relay, the contact can be opened reliably during reverse flow.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the operating principle of the first embodiment.

FIG. 3 is a diagram showing 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 operating 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 operating principle of the fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solar battery 2 Storage battery 5 Reverse current prevention device 6 Reverse current prevention diode 7 Contact point 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)

Claims (5)

[Claims] 1. A coil and a contact that is closed when a current flows in a certain direction in the coil are connected in series, and a diode is connected in parallel to the contact in the forward direction, and the current flows in the reverse direction. A backflow prevention device comprising a coil current suppressing circuit for suppressing a current flowing through the coil when the coil is reversed. 2. The backflow prevention device according to claim 1, wherein the coil current suppressing circuit includes a diode connected in parallel and in the reverse direction to the coil. 3. A series circuit, in which the coil current suppressing circuit includes a capacitor or a diode and an auxiliary coil that generates a magnetic field in a direction opposite to the magnetic field generated by the coil with respect to the contact, is connected in parallel to the coil. The backflow prevention device according to claim 1, which is configured as follows. 4. The backflow prevention device according to claim 1, wherein the coil current suppressing circuit includes an inductance connected in series with the coil. 5. The backflow prevention circuit according to any one of claims 1 to 4 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.