JP6325802B2 - Backflow prevention circuit and junction box for photovoltaic power generation - Google Patents

Description

  The present invention relates to a backflow prevention circuit for preventing backflow of current in a DC circuit, and a connection box for photovoltaic power generation.

In solar power generation, DC power sent from a plurality of solar cell strings is integrated and sent to an inverter to generate AC power. At that time, a junction box is used for integration of electric circuits.
This connection box for photovoltaic power generation is a mixture of solar panels that are shaded and not exposed to sunlight, and solar panels that are exposed to sufficient sunlight, because multiple solar cell strings are connected in parallel. The situation where it is connected with occurs. Therefore, when a solar cell string with a small generated voltage and a solar cell string with a large generated voltage are simply connected in parallel, a backflow occurs in which a current flows from a high generated voltage solar cell string to a low generated voltage solar cell string. The solar panel will break down.
In order to prevent this, a backflow prevention diode is interposed in each solar cell string in the junction box and connected in parallel via this diode (see, for example, Patent Document 1).

JP 2011-187807 A

  However, when the solar cell is generating power, current always flows through the backflow prevention diode, and energy loss due to the voltage drop of the diode always occurs. This contributed to a decrease in power generation efficiency of the solar power generation system.

  Therefore, in view of such a problem, the present invention is a backflow prevention circuit that can increase the power generation efficiency of photovoltaic power generation by configuring a backflow prevention circuit using an element having a lower loss than a diode, and the backflow prevention circuit. It aims at providing the junction box for photovoltaic power generation provided with the backflow prevention circuit.

In order to solve the above-described problem, the backflow prevention circuit according to the first aspect of the present invention turns on / off the negative-side electric circuit among a pair of positive-side electric circuit and negative-side electric circuit that sends current from a DC power supply. An FET element that is turned off, a control IC that controls the FET element, and a power supply circuit that supplies operation power to the control IC from the positive-side electric circuit, and the control IC has terminals corresponding to the three electrodes of the FET element. Then, the voltage of the source electrode and the drain electrode of the FET element is monitored, and if the predetermined relationship is satisfied, the operation voltage is output to the gate electrode to turn on the FET element, and if not, the function to turn off is provided. The circuit is characterized in that when the potential difference between the positive electrode circuit and the negative electrode circuit falls below a predetermined value, the power supply to the control IC is stopped and the FET element is turned off.
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According to this configuration, when the potential difference between the electric circuits falls below a predetermined value, the supply of power from the power supply circuit to the control IC is stopped, so that the FET element is turned off and the electric circuit is cut off. Therefore, in a situation where a backflow occurs in the circuit current, the circuit is interrupted and the backflow can be prevented.
Since the forward voltage drop in the ON operation state of the FET element is smaller than the forward voltage drop of the diode, the loss can be improved compared to the case where the diode is used for preventing the reverse current, and the current in the electric circuit is reduced. In such a situation that power does not flow, power is not supplied to the control IC, so that little power is consumed in the control IC.

The invention of claim 2 is a connection box for photovoltaic power generation in which solar cell strings are connected in parallel to output DC power in one circuit, and the backflow prevention according to claim 1 is provided in the electric circuit of each solar cell string. The circuit is connected.
According to this configuration, by using the FET element having a small on-resistance for preventing the backflow, the voltage drop of the electric circuit can be reduced and the power generation efficiency can be increased.

According to the backflow prevention circuit according to the present invention, since the FET element is turned off in a situation where backflow occurs in the circuit current, the circuit is interrupted to prevent backflow. Since the forward voltage drop in the ON operation state of the FET element is smaller than the forward voltage drop of the diode, the loss can be improved as compared with the case where the diode is used for preventing the backflow.
Moreover, by using this backflow prevention circuit for the backflow prevention means of the connection box for solar power generation, the voltage drop of the electric circuit can be reduced and the power generation efficiency can be increased.

It is a circuit diagram which shows an example of the connection box for solar power generation concerning this invention. FIG. 2 is an operation explanatory diagram of the backflow prevention circuit of FIG. 1, (a) is a normal state in which generated power is sent to the power conditioner, (b) is a low generated voltage, and the generated currents of other solar cell strings are backflowed. Indicates the state that is being attempted.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an example of a connection box for photovoltaic power generation according to the present invention, wherein 1 is a solar cell string in which a plurality of solar cell panels 1a are connected in series, 2 is a connection box, and 3 is a direct current to an alternating current. It is a power conditioner (PCS).

  In the connection box 2, a plurality of electric circuits 4 constituted by two cables of the positive electrode side electric circuit 4 a and the negative electrode side electric circuit 4 b connected to the individual solar cell strings 1 are introduced, and these electric circuits 4 are connected / cut off. An opening / closing means 5, a plurality of backflow prevention circuits 6 for preventing backflow of current for each solar cell string 1, and an integrated circuit 7 for connecting each circuit 4 in parallel and outputting them to the power conditioner 3 are provided. Reference numeral 8 denotes a lightning protection circuit.

The backflow prevention circuit 6 includes a first FET element M1 composed of a power MOSFET connected in series to the negative electrode side circuit 4b, a control IC 9 that controls the first FET element M1, and a power supply circuit 10 that supplies power to the control IC 9. Has been.
2A and 2B are explanatory diagrams of the operation of the backflow prevention circuit 6. FIG. 2A is a normal state in which generated power is sent to the power conditioner 3, and FIG. 2B is a power generation voltage of another solar cell string 1 with a small generated voltage. The state where the current is going to flow backward is shown, and will be described below with reference to FIG. The opening / closing means 5 is normally closed.

  As for the 1st FET element M1, the drain pole D is connected to the solar cell string 1 side of the negative electrode side electric circuit 4b, and the source pole S is connected to the power conditioner 3 side.

  The control IC 9 has terminals corresponding to the three electrodes of the first FET element M1, monitors the voltages of the source electrode S and the drain electrode D, and outputs an operating voltage to the gate electrode G if the predetermined relationship is satisfied. Turns on and turns off without output if not satisfied.

The power supply circuit 10 includes a second FET element M2 made of a MOSFET, a Zener diode ZD, and resistance elements R1 and R2 for current limiting. The second FET element M2 is disposed between the positive electrode side circuit 4a and the control IC 9, and power is supplied to the control IC 9 via the second FET element M2.
The second FET element M2 is set by the Zener voltage of the Zener diode ZD, and is controlled to be turned on / off by a constant voltage. The voltage of the electric circuit 4 (potential difference between the positive electrode circuit 4a and the negative electrode circuit 4b) is equal to or higher than a predetermined voltage. Then, the gate voltage is supplied to the first FET element M1 by turning on. Conversely, if the voltage does not reach the predetermined voltage, the power supply circuit 10 is turned off and the control IC 9 is turned off. As a result, the gate voltage is not supplied and the first FET element M1 is turned off.

Specifically, if the source electrode S voltage is higher than the drain electrode D voltage, the operating voltage is output to the gate electrode G, and if the source electrode S voltage is lower than the drain electrode D voltage, the operating voltage is not output to the gate electrode G. Therefore, while the forward current is flowing in the electric circuit 4, it is in the ON state, but even if the solar cell string 1 is generating power, if the backward current flows, the first FET element M1 is turned off and the current flows. To prevent. FIG. 2B shows this state.
Thus, since the gate voltage is controlled from the state of the source-drain voltage, backflow can be reliably prevented regardless of the power generation state of the solar cell string 1.

  In addition, since the second FET element M2 is turned off in a state where no power generation is performed such as at night, power is not supplied to the control IC 9. Therefore, when no power is generated, no standby power is generated in the control IC 9, and no power is consumed.

  Here, the difference in loss between the FET and the diode will be described. If the condition of the electric circuit 4 is 400 VDC and 10 amperes are energized, for example, the diode loss is 12 watts while the FET is 1.6 watts, which is reduced to 1/7 or less. The This value uses, for example, diode data of product number DG20AA120 and data of SiC power MOSFET (SCT2160KE).

In this way, when the potential difference between the positive electrode side circuit 4a and the negative electrode side circuit 4b falls below a predetermined value, the supply of power from the power supply circuit 10 to the control IC 9 is stopped, so the first FET element M1 is turned off and the electric circuit 4 Is cut off. Therefore, in a situation where a reverse flow occurs in the electric circuit current, the electric circuit 4 is blocked and the occurrence of the reverse flow can be prevented.
Since the forward voltage drop in the on-operation state of the first FET element M1 is smaller than the forward voltage drop of the diode, the loss can be improved compared to the case where the diode is used, and the current in the electric circuit 4 is reduced. Since no power is supplied to the control IC 9 in a situation where no current flows, the power consumed by the control IC 9 is very small. Therefore, by using a FET element having a low on-resistance for the backflow prevention circuit in the junction box 2, the voltage drop in the electric circuit can be reduced and the power generation efficiency can be increased.

  The first FET element M1 is not limited to the SiC power MOSFET, and may be any silicon, silicon carbide, or gallium nitride power MOSFET, and can lower the on-resistance as compared with the diode. Therefore, it is effective for improving the power generation efficiency.

  Although the said embodiment demonstrated the case where it uses with the connection box for photovoltaic power generation, it is not restricted to this, For example, the backflow prevention circuit of this invention is suitable also in DC switch for DC wiring, such as a storage battery.

  1 .... Solar cell string (DC power supply) 2 .... Junction box (solar power generation connection box) 3 .... Power conditioner 4 .... Electric circuit 4a ... Positive electrode side electric circuit 4b ... Negative electrode side electric circuit , 6 .. Backflow prevention circuit, 9... Control IC, 10... Power supply circuit, M1.

Claims (2)

Of a pair of electric circuits comprising a positive electrode circuit and a negative electrode circuit for sending current from a DC power supply, an FET element for turning on / off the electric circuit of the negative electrode circuit, a control IC for controlling the FET element, and the positive electrode side A power supply circuit for supplying operating power from an electric circuit to the control IC,
The control IC has terminals corresponding to the three electrodes of the FET element, monitors the voltage of the source electrode and the drain electrode of the FET element, and outputs an operating voltage to the gate electrode if a predetermined relationship is satisfied. The FET element is turned on, and if not satisfied, the FET element is turned off,
The power supply circuit stops a power supply to the control IC and turns off the FET element when a potential difference between the positive electrode circuit and the negative electrode circuit falls below a predetermined value. . It is a connection box for photovoltaic power generation in which solar battery strings are connected in parallel to output DC power in one circuit,
A connection box for photovoltaic power generation, wherein the backflow prevention circuit according to claim 1 is connected to an electric path of each solar cell string.

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