JPH09182279A - Short circuit detector for photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short circuit detector for breaking an output circuit in a photovoltaic power generation system by detecting a short circuit in the output circuit of a solar battery correctly. SOLUTION: An output circuit of a solar battery 3 includes a current sensor 5 for measuring an output current (I) and a voltage sensor 6 for measuring an output voltage (V). A state of short circuit is judged when the output current (I) is over a reference current I1 and the output voltage (V) is below a reference voltage V1 so as to break the circuit. A current operation relay and a voltage operation relay may be used as the current sensor 5 and the voltage sensor 6. In addition, a current operation-type electromagnet and a voltage operation- type electromagnet or a current coil and a voltage coil may be also used as the current sensor 5 and the voltage sensor 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short circuit detection device in a solar power generation system.

[0002]

2. Description of the Related Art A solar cell used in a solar power generation system generally has a current-voltage characteristic (I
-V characteristic), and the operation of the solar cell is controlled so as to reach the optimum operating point Pmax at which the output power becomes maximum. And this IV curve moves up and down according to the amount of solar radiation. The point on this IV curve is the operating point of the solar cell, and the position of the operating point is determined by the impedance connected to the solar cell. In normal photovoltaic power generation, the impedance is adjusted with an inverter or the like, and the output power P = IV is It is controlled to be maximum.

The IV characteristic of such a solar cell shows a constant voltage characteristic as shown on the right side of the optimum operating point Pmax when the impedance is larger than the impedance at the optimum operating point Pmax, and the impedance is infinite. When, that is, when the output terminal is opened, the current I =
0, open circuit voltage V = Vo. Further, when the impedance is smaller than the impedance at the optimum operating point Pmax, the constant current characteristic is shown as shown on the left side of the optimum operating point Pmax, and when the impedance is minimum, for example, when the output terminal is short-circuited, the short-circuit current I = Is, and the output voltage V approaches 0. (Hereinafter, described as output voltage V.apprxeq.0.) As shown, the short circuit current Is is about 110 to 120% of the optimum operating current Ip, and the difference between Is and Ip is small.

In the solar power generation system, the value of the short circuit current Is does not become so large even when a short circuit occurs in the circuit as described above, and the output current of the solar cell changes depending on the position of the sun, the weather, etc. It is difficult to detect a short circuit by the current change detection method, because it greatly changes depending on the amount of solar radiation.

As described above, since it is difficult to detect a short circuit in a photovoltaic power generation system, a short-circuit detection device is not installed in a small-scale photovoltaic power generation system, particularly in a general household system. there were. Therefore, even if a short circuit occurs, the operation is continued as it is, and there is a problem that the efficiency of the entire system is deteriorated by not outputting the electric energy generated by the short-circuited solar cell. Also, in solar power generation, the output power at the optimum operating point changes due to changes in the amount of solar radiation, dirt on the surface of the solar cell, surface temperature of the cell of the solar cell, deterioration of the capacity of the solar cell itself, etc. Therefore, it is difficult to determine whether the efficiency of the solar power generation system is decreasing. Even if it can be determined, there is a problem that the photovoltaic power generation system must be inspected to identify whether the cause is the solar radiation amount or the solar cell itself as described above or a short circuit. It was

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is possible to accurately detect a short circuit occurring in the output circuit of a solar cell and prevent a decrease in the efficiency of the entire system. The present invention is made to provide a short circuit detection device in a solar power generation system.

[0007]

SUMMARY OF THE INVENTION The present invention, which has been made to solve the above problems, provides a solar cell output circuit with a current sensor for measuring an output current and a voltage sensor for measuring an output voltage. The current sensor and the voltage sensor are connected to a determination means for determining a short circuit when the output current exceeds the reference current value and the output voltage is less than the reference voltage value. As the current sensor and the voltage sensor, as shown in the examples described later, a current operation relay and a voltage operation relay, a current operation type electromagnet and a voltage operation type electromagnet, a current coil and a voltage coil, etc. The circuit can be cut off.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an example of a preferred embodiment of the present invention will be described in detail with reference to the drawings. In the solar power generation system shown in FIG. 1, A is a solar cell unit equipped with a short-circuit detection device, 1 is an inverter, 2 is an interconnection transformer, and a plurality of solar cell units A equipped with a short-circuit detection device are connected to inverters. These outputs are connected in parallel, and these outputs are added together and connected to the system via devices such as the inverter 1 and the interconnection transformer 2. Also,
In the solar cell unit A equipped with the short circuit detection device shown in FIG. 2, 3 is a solar cell, 4 is a switch, and the output circuit of this solar cell 3 has a current sensor 5 for measuring an output current.
And a voltage sensor 6 for measuring the output voltage, and a judging means 7 for judging a short circuit based on the output current I and the output voltage V measured by the current sensor 5 and the voltage sensor 6. Is provided.

This judging means 7 is connected to the current sensor 5 and the voltage sensor 6, the output current I measured by the current sensor 5 exceeds the reference current value I ₁ , and the output voltage V measured by the voltage sensor 6 becomes It has a function of determining a short circuit when it is less than the reference voltage value V ₁ .

Next, the operation of the short-circuit detecting device in the solar power generation system of the present invention thus constructed will be described with reference to FIG. In FIG. 3, three IV characteristic curves are shown according to the amount of solar radiation, large, medium and small. This figure 3
As is clear from the above, when a short circuit occurs in the output circuit of the solar cell 1 regardless of the amount of solar radiation, the output voltage V
When ≈0, the operating point shifts to a point where the output current I is I _S1 , I _S2 , and I _S3 .

Therefore, if the reference voltage value V ₁ and the reference current value I ₁ are set as shown in FIG. 3, the shaded area (V <V ₁ , I> I ₁ ) in FIG. When the operating point is entered, the determination means 7 determines that a short circuit has occurred, and when the amount of solar radiation at which the photovoltaic power generation system operates effectively is large and medium, the output voltage V is approximately 0 and the output current I is I _S1. , I _S2 , it is possible to accurately determine the short circuit. The reference voltage value V ₁ and the reference current value I ₁ may be empirically determined.

In the example of FIG. 3, when the amount of solar radiation is small and the power generation of the photovoltaic power generation system is very small, the operating point at the time of short circuit is output voltage V≈0 and output current I <I ₁ . Although it is not possible to detect a short circuit because it is out of the short circuit determination area, in this case, there is no particular problem because the output of the solar power generation system is small, and it is possible to make a determination if the amount of solar radiation increases again, so there is no problem. Further, when there is no solar radiation like at night, the operating point comes to the point (0, 0) in FIG. 3, but in this case, the output current I becomes the reference current value I ₁ or less, It is never judged as a short circuit. In this way, according to the present invention, the short circuit of the output circuit can be distinguished from the fluctuation of the solar radiation amount or the normal fluctuation of the impedance, and can be accurately detected without the risk of malfunction. In addition, in FIG. 2, by informing of a short circuit based on the abnormal signal from the determination means 7, it is possible to take necessary measures such as repair at an early stage. Alternatively, it is possible to prevent a fault current from flowing to related equipment such as an inverter by operating the switch 4 in response to a signal from the determination means 7 to disconnect the fault circuit, and the switch 4 is turned off.
By checking whether it is N or OFF, it can be determined that the cause of the efficiency decrease is a short circuit, and the short-circuited circuit can be specified.

[0013]

【Example】

[Embodiment 1] FIG. 5 is a circuit diagram showing a first embodiment of the present invention. 3 is a solar cell and 4 is a breaker used as a switch. In this embodiment, an exciting coil 5a of a current operation relay is incorporated as the current sensor 5, and an exciting coil 6a of a voltage operation relay is incorporated as the voltage sensor 6.
8 is a contact of current operation relay, 9 is b of voltage operation relay
It is a contact point. These contacts 8 and 9 are connected in series so that a current flows from a capacitor 11 to a trip coil 10 of a breaker when both contacts are closed.

In this embodiment, the output current I of the solar cell 3 is
When the current exceeds the reference current value I ₁ , the a-contact 8 of the current operation relay closes. Further, when the output voltage V is less than the reference voltage value V ₁ , the b contact 9 of the voltage operation relay is closed. Therefore, when the output of the solar cell 3 enters the short circuit determination region of FIG. 3 due to a short circuit, a current flows from the capacitor 11 to the trip coil 10 of the breaker, and the breaker trip mechanism operates to open the contact of the breaker. . Manual operation is required to restore the breaker. Reference numeral 12 is a backflow prevention diode, which is provided to prevent discharge of the capacitor 11 due to a short circuit of the output circuit of the solar cell 3 and to keep the excitation energy in the trip coil 10 at all times.

[Second Embodiment] FIG. 6 is a circuit diagram showing a second embodiment of the present invention. In this embodiment, a current-operated electromagnet 5b is incorporated as the current sensor 5, and a voltage-operated electromagnet 6b is incorporated as the voltage sensor 6. By setting the winding direction of the coil in the opposite direction, when the output current I of the solar cell 3 exceeds the reference current value I ₁ , the iron core 13
Direction of the force F ₂ acting on the output voltage V and the reference voltage value V ₁
The direction is opposite to the direction of the force F ₁ acting on the iron core 13 when the force exceeds.

FIG. 7 is a conceptual diagram showing the relationship between these forces F ₁ and F ₂ and the contacts, and shows that the contacts are opened when F ₁ <F ₂ . In this embodiment, when the output of the solar cell 3 enters the short circuit judgment region of FIG. 3 due to a short circuit, the output current I exceeds the reference current value I ₁ , so that the force F ₂ acts on the contact and the output voltage V is the reference. Since the voltage value V ₁ is not exceeded, the force F ₁ ≈0. Therefore, at this time, F ₁ <F ₂ and the contacts are opened.

[Third Embodiment] FIG. 8 is a circuit diagram showing a third embodiment of the present invention. This embodiment shows an example in which a general circuit breaker is used to break the circuit. That is, when the output current I exceeds the reference current value I ₁ , the current-operated electromagnet 5c attracts the iron piece 14, and the trigger lever 15 of the breaker is pushed in the direction of the arrow to be opened by the tripping mechanism. However, if the output voltage V is the reference voltage value V ₁
If it exceeds, the voltage-operated electromagnet 6c moves the lock bar 16 upwards against the spring 17 and hinders the movement of the iron piece 14. Therefore, when both the output current I and the output voltage V exceed the reference value, the trigger lever 15 is not moved.

On the other hand, when the circuit is short-circuited, the output voltage V does not exceed the reference voltage value V _1. Therefore, the lock bar 16 does not operate and is pulled back downward by the spring 17. Therefore, when a short circuit occurs, the current-operated electromagnet 5c attracts the iron piece 14 and pushes the trigger lever 15 in the direction of the arrow to open the contact.

[Fourth Embodiment] FIG. 9 is a circuit diagram showing a fourth embodiment of the present invention. This embodiment shows a dashpot type short-circuit detecting device, in which 18 is a yoke, 19 is an armature pivotally attached to its end, and 20 is a cylinder. Inside the cylinder 20, a spring 21 provides a pole piece.
An ejected plunger 23 is housed on the side opposite to 22. Surrounding the cylinder 20 is a current coil 5d and a voltage coil 6d
And are double installed.

[0020] from these current coil 5d and the voltage coil 6d, and the magnetomotive force F _V by magnetomotive force F _I and the voltage by the current wound to act in the opposite direction, and solar by short cell 3
When the output of the input enters the short circuit judgment area of Fig. 3, F _I > F _V
It is set to be. Therefore, when a short circuit occurs, F _I
The force of −F _V causes the plunger 23 to be attracted to the pole piece 22, which causes the armature 19 to act against the spring 24, tripping a conventional circuit breaker and breaking the circuit.

[Fifth Embodiment] FIG. 10 is a circuit diagram showing a fifth embodiment of the present invention. In this embodiment, the dashpot of the fourth embodiment is replaced with an iron core 25. In addition, as shown in FIG. 11, the current coil 5d and the voltage coil 6d are connected to the iron core.
It may be installed separately in the longitudinal direction of 25. The magnetic flux produced by the magnetic flux and the voltage coil 6d by current coil 5d in each case Yes set to be reversed, when the output of the solar cell 3 has entered the short determination area in FIG. 3, the F _I -F _V Similar to the fourth embodiment, the force pulls the armature 19 against the spring 24 and trips the circuit breaker to break the circuit.

[0022]

As described above, according to the present invention, the short circuit of the output circuit of the solar cell is distinguished from the fluctuation of the solar radiation amount or the normal fluctuation of the impedance and is accurately detected. Is possible. Therefore, it is possible to prevent a decrease in the efficiency of the photovoltaic power generation system and to reduce the reliability because the necessary measures such as inspection and repair can be performed early by notifying the short circuit with an alarm device based on the abnormal signal of the determination means. It can be expected to improve the sex. In addition, as shown in each example, the fault current can be interrupted by opening the switch of the circuit immediately when the short circuit is detected, and the circuit in which the short circuit fault has occurred can be identified by the operating state of the switch. It has an excellent effect that it can be done.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a main part of an embodiment of the present invention.

FIG. 3 is a graph for explaining an embodiment of the present invention.

FIG. 4 is a graph showing general voltage-current characteristics of a solar cell.

FIG. 5 is a circuit diagram showing a first embodiment of the present invention.

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

FIG. 7 is a conceptual diagram showing a relationship between a force F ₂ caused by a current and a force F ₁ caused by a voltage.

FIG. 8 is a circuit diagram showing a third embodiment of the present invention.

FIG. 9 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 10 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 11 is a circuit diagram showing a modification of the fifth embodiment.

[Explanation of symbols]

 1 Inverter 2 Interconnection transformer 3 Solar cell 4 Switch 5 Current sensor 5a Current operation relay exciting coil 5b Current operation type electromagnet 5c Current operation type electromagnet 5d Current coil 6 Voltage sensor 6a Voltage operation relay exciting coil 6b Voltage operation type Electromagnet 6c Voltage-operated electromagnet 6d Voltage coil 7 Judgment means 8 A contact of current operation relay 9 B contact of voltage operation relay 10 Breaker trip coil 11 Capacitor 12 Reverse current prevention diode 13 Iron core 14 Iron piece 15 Breaker trigger lever 16 Lock bar 17 Spring 18 Yoke 19 Armature 20 Cylinder 21 Spring 22 Pole piece 23 Plunger 24 Spring 25 Iron core

Claims (4)

[Claims] 1. A solar cell output circuit is provided with a current sensor for measuring an output current and a voltage sensor for measuring an output voltage, and the current sensor and the voltage sensor have an output current exceeding a reference current value, and A short-circuit detection device in a photovoltaic power generation system, characterized in that a determination means for determining a short-circuit when an output voltage is less than a reference voltage value is connected. 2. The short circuit detection device in the solar power generation system according to claim 1, wherein the current sensor and the voltage sensor are a current operation relay and a voltage operation relay. 3. The short-circuit detecting device in the solar power generation system according to claim 1, wherein the current sensor and the voltage sensor are a current-operated electromagnet and a voltage-operated electromagnet. 4. The short circuit detection device in the solar power generation system according to claim 1, wherein the current sensor and the voltage sensor are a current coil and a voltage coil.