JP7537238B2 - Protection device, power conversion system, and protection method - Google Patents

Description

The present disclosure relates to a protection device, a power conversion system, and a protection method.

Patent Document 1 describes a first relay provided in a first current path that outputs power from a solar cell and opens and closes the first current path, a second relay provided in a second current path that short-circuits the positive and negative outputs of the solar cell and opens and closes the second current path, a third relay provided in a third current path that short-circuits the positive and negative outputs of the solar cell and opens and closes the third current path, an arc signal detection means that detects an arc signal indicating the occurrence of an arc from the first current path, and an arc presence/absence determination means that determines the presence or absence of an arc based on the arc signal in an arc presence/absence determination state in which the first relay is in a closed state and the second and third relays are in an open state. means for determining whether the arc is a parallel arc or a series arc based on an arc signal in an arc identification state in which the first and second relays are closed and the third relay is open; and control means for placing the first to third relays in the arc identification state when the arc presence/absence determination means determines that an arc has occurred, placing the first relay in the open state from the arc identification state when the arc identification means determines that the arc is a series arc, and placing the third relay in the closed state from the arc identification state when the arc identification means determines that the arc is a parallel arc.

JP 2016-32369 A

This disclosure provides a protection device that is effective in reliably protecting a solar power generation system from heat generation due to arcs.

A protection device according to one aspect of the present disclosure includes an arc detection unit that detects an arc in a solar cell string connected to a load, an arc extinction control unit that performs series arc extinction control to cut off a series current path that passes a current through the solar cell string via the load when an arc is detected by the arc detection unit, and parallel arc extinction control to conduct a parallel current path that passes a current through the solar cell string without passing through the load, a series arc detection unit that detects a series arc in the solar cell string when an arc is detected by the arc detection unit in a state in which the series current path is cut off and the parallel current path is conducted after the series arc extinction control and the parallel arc extinction control, a parallel arc detection unit that detects a parallel arc in the solar cell string when an arc is detected by the arc detection unit in a state in which both the series current path and the parallel current path are cut off after the series arc extinction control and the parallel arc extinction control, and a protection control unit that cuts off the parallel current path when a series arc is detected in the solar cell string and conducts the parallel current path when a parallel arc is detected in the solar cell string.

The series arc detection unit may wait for the arc detection unit to detect an arc until a predetermined length of series arc waiting period has elapsed when the series electric path is interrupted and the parallel electric path is conductive, and the parallel arc detection unit may wait for the arc detection unit to detect an arc until a predetermined length of parallel arc waiting period has elapsed when both the series electric path and the parallel electric path are interrupted.

The arc extinguishing control unit executes parallel arc extinguishing control after the series arc extinguishing control, and the series arc detection unit waits for the arc detection unit to detect an arc until a series arc wait period has elapsed after the parallel arc extinguishing control, and if the series arc wait period has elapsed without the arc detection unit detecting an arc, the parallel arc detection unit may interrupt the parallel circuit and then wait for the arc detection unit to detect an arc until the parallel arc wait period has elapsed.

The protection device may further include a recovery control unit that restores electrical continuity to the series circuit when the series arc standby period has elapsed without an arc being detected by the arc detection unit and the parallel arc standby period has elapsed without an arc being detected by the arc detection unit.

The protection device further includes a second arc detection unit that detects an arc in the second solar cell string connected to the load, and the extinguishing control unit executes series extinguishing control and parallel extinguishing control when an arc is not detected by the second arc detection unit and an arc is detected by the arc detection unit, and executes second series extinguishing control to interrupt the second series current path that passes current to the second solar cell string through the load and second parallel extinguishing control to conduct the second parallel current path that passes current to the second solar cell string without passing through the load when an arc is not detected by the arc detection unit and an arc is detected by the second arc detection unit, and the series arc detection unit executes the second series extinguishing control and the second parallel extinguishing control. After the control, when the second series electric path is interrupted and the second parallel electric path is conductive, the second arc detection unit detects a series arc in the second solar cell string, and the parallel arc detection unit detects a parallel arc in the second solar cell string when an arc is detected by the second arc detection unit with both the second series electric path and the second parallel electric path interrupted after the second series arc-extinguishing control and the second parallel arc-extinguishing control, and the protection control unit may interrupt the second parallel electric path when a series arc in the second solar cell string is detected, and may make the second parallel electric path conductive when a parallel arc in the second solar cell string is detected.

The protection control unit may interrupt both the series circuit and the second series circuit when an arc is detected by the arc detection unit and an arc is detected by the second arc detection unit.

The arc detection unit includes a current sensor that detects the current flowing through the solar cell string and a voltage sensor that detects the voltage applied to the load by the solar cell string. When the series circuit is interrupted and the parallel circuit is conductive, the arc may be detected by the current sensor, and when both the series circuit and the parallel circuit are interrupted, the arc may be detected by the voltage sensor.

The arc detection unit may detect the voltage noise level using a voltage sensor.

The arc detection unit may detect the voltage drop level using a voltage sensor.

The arc detection unit may include a current sensor that detects the current flowing through the solar cell string, and a bypass circuit that passes AC current through the solar cell string via the current sensor even when both the series and parallel current paths are interrupted.

The bypass circuit may include a reactor, a capacitor, and a resistor connected in series with each other.

A power conversion system according to another aspect of the present disclosure includes the above-mentioned protection device and the above-mentioned load, which is a power conversion circuit that converts the power output by the solar cell string into AC power.

A protection method according to yet another aspect of the present disclosure includes, when an arc is detected by an arc detection unit in a solar cell string connected to a load, executing a series arc-extinguishing control for interrupting a series current path that passes a current to the solar cell string through the load, and a parallel arc-extinguishing control for conducting a parallel current path that passes a current to the solar cell string without passing through the load; detecting a series arc in the solar cell string when an arc is detected by the arc detection unit in a state in which the series current path is interrupted and the parallel current path is conducted after the series arc-extinguishing control and the parallel arc-extinguishing control; detecting a parallel arc in the solar cell string when an arc is detected by the arc detection unit in a state in which both the series current path and the parallel current path are interrupted after the series arc-extinguishing control and the parallel arc-extinguishing control; and interrupting the parallel current path when a series arc is detected in the solar cell string, and conducting the parallel current path when a parallel arc is detected in the solar cell string.

This disclosure makes it possible to provide a protective device that is effective in achieving both efficient use of solar cell modules and arc suppression.

FIG. 1 is a schematic diagram illustrating a configuration of a power generation system. FIG. 2 is a block diagram illustrating an example of a functional configuration of a controller. FIG. 2 is a block diagram illustrating a hardware configuration of a controller. FIG. 13 is a schematic diagram showing a modified example of the power generation system. FIG. 2 is a schematic diagram illustrating a configuration of a bypass circuit. FIG. 13 is a schematic diagram showing a further modified example of the power generation system. FIG. 13 is a schematic diagram showing a further modified example of the power generation system. 4 is a flowchart illustrating a procedure for protecting the power generation system. 4 is a flowchart illustrating a procedure for protecting the power generation system. 10 is a flowchart showing a modified example of the procedure for protecting the power generation system.

The following describes the embodiments in detail with reference to the drawings. In the description, the same elements or elements having the same functions are given the same reference numerals, and duplicate descriptions are omitted.

[Power generation system]
1 is a photovoltaic power generation system that generates photovoltaic power, converts the resulting DC power into AC power, and outputs the AC power. The power generation system 1 includes a plurality of strings 2 and 3 and a power conversion system 4.

String 2 (solar cell string) has one or more solar cell modules 21, a positive string wire 23p, and a negative string wire 23n. FIG. 1 shows a case where string 2 has multiple solar cell modules 21, but string 2 only needs to have at least one solar cell module 21.

Each of the multiple solar cell modules 21 has a positive electrode 21p and a negative electrode 21n. Each solar cell module 21 includes multiple solar cell cells connected in series with each other, and outputs DC power generated by the multiple solar cell cells to the positive electrode 21p and the negative electrode 21n. The multiple solar cell modules 21 are connected in series with each other. For example, at the connection portion between the solar cell modules 21, the positive electrode 21p of one solar cell module 21 is connected to the negative electrode 21n of the other solar cell module 21. The positive electrode string wire 23p connects the positive electrode 21p to a load. The negative electrode string wire 23n connects the negative electrode 21n to a load. The load is, for example, a power conversion circuit 43 described below.

As an example, the positive electrode string wire 23p connects the positive electrode 21p of the solar cell module 21 located on the most positive electrode side among the multiple solar cell modules 21 (hereinafter referred to as the "positive electrode solar cell module 21") to the power conditioning system 40. The negative electrode string wire 23n connects the negative electrode 21n of the solar cell module 21 located on the most negative electrode side among the multiple solar cell modules 21 (hereinafter referred to as the "negative electrode solar cell module 21") to the power conditioning system 40.

Note that connecting includes not only direct connection but also indirect connection. As described below, the positive string wire 23p is indirectly connected to the power conditioning system 40 via the protection device 50. Similarly, the negative string wire 23n is indirectly connected to the power conditioning system 40 via the protection device 50.

The positive string wire 23p is indirectly connected to the positive electrode 21p of another solar cell module 21 via the positive terminal solar cell module 21. Similarly, the negative string wire 23n is indirectly connected to the negative electrode 21n of another solar cell module 21 via the negative terminal solar cell module 21. Therefore, the positive string wire 23p connects the positive electrode 21p of each solar cell module 21 to the power conditioning system 40, and the negative string wire 23n connects the negative electrode 21n of each solar cell module 21 to the power conditioning system 40.

String 3 (second solar cell string), like string 2, has one or more solar cell modules 31 (second solar cell modules), a positive string line 33p (second positive string line), and a negative string line 33n (second negative string line). Although FIG. 1 shows a case where string 3 has multiple solar cell modules 31, string 3 only needs to have at least one solar cell module 31.

The configuration and function of the multiple solar cell modules 31 are the same as those of the multiple solar cell modules 21. Each of the multiple solar cell modules 31 has a positive electrode 31p (second positive electrode) and a negative electrode 31n (second negative electrode) like each of the multiple solar cell modules 21. The positive electrode string wire 33p connects the positive electrode 31p to the load, and the negative electrode string wire 33n connects the negative electrode 31n to the load. For example, the positive electrode string wire 33p connects the positive electrode 31p of the solar cell module 31 at the positive electrode end to the power conditioning system 40, and the negative electrode string wire 33n connects the negative electrode 31n of the solar cell module 31 at the negative electrode end to the power conditioning system 40.

For example, the power conversion system 4 includes a power conditioning system 40 and a protection device 50. The power conditioning system 40 converts the DC power output by the string 2 to the positive string line 23p and the negative string line 23n, and the DC power output by the string 3 to the positive string line 33p and the negative string line 33n, into AC power.

The power conditioning system 40 has a positive input terminal 41p, a negative input terminal 41n, a positive input terminal 42p, a negative input terminal 42n, and a power conversion circuit 43. The positive input terminal 41p is connected to the positive string line 23p via a protection device 50, and the negative input terminal 41n is connected to the negative string line 23n via a protection device 50. The positive input terminal 42p is connected to the positive string line 33p via the protection device 50, and the negative input terminal 42n is connected to the negative string line 33n via the protection device 50.

The power conversion circuit 43 converts the DC power input to the positive input terminal 41p and the negative input terminal 41n and the DC power input to the positive input terminal 42p and the negative input terminal 42n into DC power. The power conversion circuit 43 has a converter circuit 44, a converter circuit 45, and an inverter circuit 46.

Each of the converter circuits 44 and 45 performs power conversion between primary-side DC power and secondary-side DC power by switching on and off a number of switching elements. The primary side of the converter circuit 44 is connected to the positive input terminal 41p and the negative input terminal 41n, and the primary side of the converter circuit 45 is connected to the positive input terminal 42p and the negative input terminal 42n. The secondary sides of the converter circuits 44 and 45 are connected in parallel to the primary side of the inverter circuit 46.

The inverter circuit 46 performs power conversion between DC power on the primary side and AC power on the secondary side by switching multiple switching elements on and off. This converts the DC power output by string 2 and the DC power output by string 3 into AC power.

The protection device 50 is interposed between the strings 2, 3 and the power conditioning system 40, and protects the power generation system 1 from excessive heat generation caused by arc generation. When a series arc occurs in the string 2, it is necessary to cut off both the series circuit R01 that passes current to the string 2 through a load (e.g., the power conversion circuit 43) and the parallel circuit R02 that passes current to the string 2 without passing through a load. On the other hand, when a parallel arc occurs in the string 2, it is necessary to form the parallel circuit R02. Note that a series arc is an arc that occurs at an incomplete break point, and a parallel arc is an arc that occurs at an incomplete short-circuit point. For example, a series arc in the string 2 may occur at an incomplete break point in the positive string wire 23p or the negative string wire 23n. A parallel arc in the string 2 may occur at an incomplete short-circuit point in the positive string wire 23p or the negative string wire 23n.

As mentioned above, how string 2 should be protected differs depending on whether a series arc or a parallel arc has occurred, so it is important to be able to identify with high reliability whether a series arc or a parallel arc has occurred in string 2.

In response to this, the protection device 50 is configured to execute a series arc-extinguishing control for interrupting the series electric circuit R01 and a parallel arc-extinguishing control for forming a parallel electric circuit R02 when an arc is detected by the arc detection unit after the series arc-extinguishing control and the parallel arc-extinguishing control, detect the occurrence of a series arc in string 2 when an arc is detected by the arc detection unit in a state in which the series electric circuit R01 is interrupted and the parallel electric circuit R02 is formed, detect the occurrence of a parallel arc in string 2 when an arc is detected by the arc detection unit in a state in which both the series electric circuit R01 and the parallel electric circuit R02 are interrupted after the series arc-extinguishing control and the parallel arc-extinguishing control, and interrupt the parallel electric circuit R02 when a series arc is detected in string 2, and make the parallel electric circuit R02 conductive when a parallel arc is detected in string 2.

When the series circuit is interrupted and the parallel circuit is conductive, a parallel arc does not occur. Based on the result of detecting an arc in such a state, a series arc can be detected with high reliability. Also, when both the series circuit and the parallel circuit are interrupted, a series arc does not occur. Based on the result of detecting an arc in such a state, a parallel arc can be detected with high reliability. When a series arc is detected, both the series circuit and the parallel circuit are interrupted, and when a parallel arc is detected, the parallel circuit is made conductive. Based on the result of identifying whether it is a series arc or a parallel arc with high reliability, the solar cell string can be protected from heat generation due to arcing with high reliability. Therefore, it is effective in protecting a solar power generation system from heat generation due to arcing with high reliability.

As an example, the protection device 50 has a positive input terminal 51p, a negative input terminal 51n, a positive input terminal 52p, a negative input terminal 52n, a positive output terminal 53p, a negative output terminal 53n, a positive output terminal 54p, a negative output terminal 54n, a positive relay line 55p, a negative relay line 55n, a positive relay line 56p, and a negative relay line 56n.

The positive input terminal 51p is connected to the positive string line 23p of string 2, and the negative input terminal 51n is connected to the negative string line 23n of string 2. The positive input terminal 52p is connected to the positive string line 33p of string 3, and the negative input terminal 52n is connected to the negative string line 33n of string 3.

The positive output terminal 53p is connected to the positive input terminal 41p of the power conditioning system 40 by a positive relay wire 81p, and the negative output terminal 53n is connected to the negative input terminal 41n of the power conditioning system 40 by a negative relay wire 81n. The positive output terminal 54p is connected to the positive input terminal 42p of the power conditioning system 40 by a positive relay wire 82p, and the negative output terminal 54n is connected to the negative input terminal 42n of the power conditioning system 40 by a negative relay wire 82n.

The positive relay wire 55p connects the positive input terminal 51p and the positive output terminal 53p within the protection device 50, and the negative relay wire 55n connects the negative input terminal 51n and the negative output terminal 53n within the protection device 50. The positive relay wire 56p connects the positive input terminal 52p and the positive output terminal 54p within the protection device 50, and the negative relay wire 56n connects the negative input terminal 52n and the negative output terminal 54n within the protection device 50.

As a result, as described above, the positive input terminal 41p and the negative input terminal 41n of the power conditioning system 40 are connected to the positive string wire 23p and the negative string wire 23n of the string 2, respectively, via the protection device 50. The positive input terminal 42p and the negative input terminal 42n of the power conditioning system 40 are connected to the positive string wire 33p and the negative string wire 33n of the string 3, respectively, via the protection device 50.

The protection device 50 further includes a series switch 61, a parallel switch 62, a series switch 63, a parallel switch 64, arc detection units AS1 and AS2, and a controller 70.

The series switch 61 switches between an ON state in which the series electric circuit R01 is conductive and an OFF state in which the series electric circuit R01 is interrupted in response to a control signal. For example, the series switch 61 is provided in the positive relay line 55p, and switches ON/OFF between the positive input terminal 51p and the positive output terminal 53p in response to a control signal. The series switch 61 may also be provided in the negative relay line 55n.

The parallel switch 62 switches between an ON state in which the parallel electric circuit R02 is conductive and an OFF state in which the parallel electric circuit R02 is interrupted in response to a control signal. For example, the parallel switch 62 is provided between the positive relay line 55p and the negative relay line 55n, between the positive input terminal 51p and the series switch 61. This makes it possible to make the parallel electric circuit R02 conductive even when the series switch 61 is in the OFF state.

The series switch 63 switches between an ON state in which the series circuit R11 (second series circuit) that passes current through the string 3 via a load (e.g., the power conversion circuit 43) and an OFF state in which the series circuit R11 is interrupted in response to a control signal. For example, the series switch 63 is provided on the positive relay line 56p, and switches ON/OFF between the positive input terminal 52p and the positive output terminal 54p in response to a control signal. The series switch 63 may be provided on the negative relay line 56n. The series switches 61 and 63 may be configured such that the series switch 63 switches ON/OFF in conjunction with the series switch 61, and the series switch 61 switches ON/OFF in conjunction with the series switch 63. For example, one contact of an electromagnetic switch that switches ON/OFF of multiple contacts with one coil may be used as the series switch 61, and the other contact may be used as the series switch 63.

The parallel switch 64 switches between an ON state in which the parallel circuit R12 (second parallel circuit) that passes current to the string 3 without passing through a load (e.g., the power conversion circuit 43) is turned on and an OFF state in which the parallel circuit R12 is cut off in response to a control signal. For example, the parallel switch 64 is provided between the positive input terminal 52p and the series switch 63, between the positive relay line 56p and the negative relay line 56n. This makes it possible to turn on the parallel circuit R12 even when the series switch 63 is in the OFF state. Specific examples of the series switches 61, 63 and the parallel switches 62, 64 include electromagnetic relays. The parallel switches 62, 64 may be configured such that the parallel switch 64 switches on and off in conjunction with the parallel switch 62, and the parallel switch 62 switches on and off in conjunction with the parallel switch 64. For example, one contact of an electromagnetic switch that switches multiple contacts on and off with one coil may be used as parallel switch 62, and the other contact may be used as parallel switch 64.

The arc detection unit AS1 detects an arc in string 2. As an example, the arc detection unit AS1 has a current sensor 65 and a voltage sensor 67. The current sensor 65 detects the current flowing through string 2. As an example, the current sensor 65 is provided on the positive relay line 55p between the parallel switch 62 and the positive input terminal 51p. This makes it possible for the current sensor 65 to detect the current flowing through string 2. The current sensor 65 may also be provided on the negative relay line 55n between the parallel switch 62 and the negative input terminal 51n. In this case as well, it becomes possible for the current sensor 65 to detect the current flowing through string 2.

The voltage sensor 67 detects the voltage applied by the string 2 to the power conversion circuit 43. As an example, the voltage sensor 67 is provided between the positive relay wire 55p and the negative relay wire 55n, between the positive input terminal 51p and the series switch 61. This makes it possible to detect the voltage between the positive string wire 23p and the negative string wire 23n even when the series switch 61 is in the off state.

When the series electric path R01 is conducting and the parallel electric path R02 is interrupted, the arc detection unit AS1 detects an arc by the current sensor 65 and also detects an arc by the voltage sensor 67. When the series electric path R01 is interrupted and the parallel electric path R02 is conducting, the arc detection unit AS1 detects an arc by the current sensor 65, and when both the series electric path R01 and the parallel electric path R02 are interrupted, the arc detection unit AS1 detects an arc by the voltage sensor 67. Hereinafter, the state in which the series electric path R01 is conducting and the parallel electric path R02 is interrupted is referred to as the "normal state", the state in which the series electric path R01 is interrupted and the parallel electric path R02 is conducting is referred to as the "series verification state", and the state in which both the series electric path R01 and the parallel electric path R02 are interrupted is referred to as the "parallel verification state".

In the normal state, the arc detection unit AS1 may detect the current noise level by the current sensor 65, may detect the voltage noise level by the voltage sensor 67, or may detect the voltage drop level by the voltage sensor 67, as a signal indicating the occurrence of an arc. In the series verification state, the arc detection unit AS1 may detect the current noise level by the current sensor 65, as a signal indicating the occurrence of an arc. In the parallel verification state, the arc detection unit AS1 may detect the voltage noise level by the voltage sensor 67, or may detect the voltage drop level by the voltage sensor 67.

The arc detection unit AS2 (second arc detection unit) detects an arc in string 3. As an example, the arc detection unit AS2 has a current sensor 66 and a voltage sensor 68. The current sensor 66 detects the current flowing through string 3. As an example, the current sensor 66 is provided on the positive relay line 56p between the parallel switch 64 and the positive input terminal 52p. This makes it possible for the current sensor 66 to detect the current flowing through string 3. The current sensor 66 may also be provided on the negative relay line 56n between the parallel switch 64 and the negative input terminal 52n. In this case as well, it becomes possible for the current sensor 66 to detect the current flowing through string 3.

The voltage sensor 68 detects the voltage applied by the string 3 to the power conversion circuit 43. As an example, the voltage sensor 68 is provided between the positive relay line 56p and the negative relay line 56n between the positive input terminal 52p and the series switch 63. This makes it possible to detect the voltage between the positive string line 33p and the negative string line 33n even when the series switch 63 is in the off state.

When the series electric path R11 is conductive and the parallel electric path R12 is interrupted, the arc detection unit AS2 detects an arc by the current sensor 66 and also detects an arc by the voltage sensor 68. When the series electric path R11 is interrupted and the parallel electric path R12 is conductive, the arc detection unit AS2 detects an arc by the current sensor 66, and when both the series electric path R11 and the parallel electric path R12 are interrupted, the arc detection unit AS2 detects an arc by the voltage sensor 68. Hereinafter, the state in which the series electric path R11 is conductive and the parallel electric path R12 is interrupted is referred to as the "normal state", the state in which the series electric path R11 is interrupted and the parallel electric path R12 is conductive is referred to as the "second series verification state", and the state in which both the series electric path R11 and the parallel electric path R12 are interrupted is referred to as the "second parallel verification state".

In the normal state, the arc detection unit AS2 may detect the current noise level by the current sensor 66, may detect the voltage noise level by the voltage sensor 68, or may detect the voltage drop level by the voltage sensor 68, as a signal indicating the occurrence of an arc. In the second series verification state, the arc detection unit AS2 may detect the current noise level by the current sensor 66, as a signal indicating the occurrence of an arc. In the second parallel verification state, the arc detection unit AS2 may detect the voltage noise level by the voltage sensor 68, or may detect the voltage drop level by the voltage sensor 68.

The controller 70 is a control computer that switches the series switch 61, the parallel switch 62, the series switch 63, and the parallel switch 64 on and off based on the results of the arc detection by the arc detection units AS1 and AS2. The controller 70 is configured to execute the series extinction control and the parallel extinction control when an arc is detected by the arc detection unit AS1, to detect the occurrence of a series arc in string 2 when an arc is detected by the arc detection unit AS1 in the series verification state after the series extinction control and the parallel extinction control, to detect the occurrence of a parallel arc in string 2 when an arc is detected by the arc detection unit AS1 in the parallel verification state after the series extinction control and the parallel extinction control, to interrupt the parallel electric circuit R02 when a series arc is detected in string 2, and to turn on the parallel electric circuit R02 when a parallel arc is detected in string 2. For example, as shown in FIG. 2, the controller 70 has, as its functional configuration (hereinafter referred to as "functional blocks"), an arc extinguishing control unit 71, a series arc detection unit 72, a protection control unit 73, and a parallel arc detection unit 75.

The extinguishing control unit 71 executes the above-mentioned series extinguishing control and parallel extinguishing control when an arc is detected by the arc detection unit AS1. Specific examples of when an arc is detected by the arc detection unit AS1 include when the noise level of the current detected by the current sensor 65 exceeds a predetermined level, when the noise level of the voltage detected by the voltage sensor 67 exceeds a predetermined level, when the voltage drop level detected by the voltage sensor 67 exceeds a predetermined level, etc.

The extinction control unit 71 may execute parallel extinction control after series extinction control, or may execute series extinction control after parallel extinction control. As an example, the extinction control unit 71 executes parallel extinction control after series extinction control. In this case, the protection device 50 enters the above-mentioned series verification state after the execution of parallel extinction control. In series extinction control, the extinction control unit 71 switches, for example, the series switch 61 from an on state to an off state. In parallel extinction control, the extinction control unit 71 switches, for example, the parallel switch 62 from an off state to an on state.

When an arc is detected by the arc detection unit AS1, executing the series extinction control and the parallel extinction control means executing the series extinction control and the parallel extinction control in at least some of the cases when an arc is detected by the arc detection unit AS1. Therefore, even if an arc is detected by the arc detection unit AS1, the extinction control unit 71 does not need to execute the series extinction control and the parallel extinction control if other predetermined conditions are not satisfied.

For example, the extinction control unit 71 may execute series extinction control and parallel extinction control when an arc is not detected by the arc detection unit AS2 and an arc is detected by the arc detection unit AS1, and execute second series extinction control and second parallel extinction control when an arc is not detected by the arc detection unit AS1 and an arc is detected by the arc detection unit AS2. The second series extinction control is a control for interrupting the series electric circuit R11, and the second parallel extinction control is a control for conducting the parallel electric circuit R12. Specific examples of cases in which an arc is detected by the arc detection unit AS2 include a case in which the noise level of the current detected by the current sensor 66 exceeds a predetermined level, a case in which the noise level of the voltage detected by the voltage sensor 68 exceeds a predetermined level, and a case in which the voltage drop level detected by the voltage sensor 68 exceeds a predetermined level.

The extinction control unit 71 may execute the second parallel extinction control after the second series extinction control, or may execute the second series extinction control after the second parallel extinction control. As an example, the extinction control unit 71 executes the second parallel extinction control after the second series extinction control. In the second series extinction control, the extinction control unit 71 switches the series switch 63 from an on state to an off state, for example. In the second parallel extinction control, the extinction control unit 71 switches the parallel switch 64 from an off state to an on state, for example.

After the series extinction control and the parallel extinction control, when an arc is detected by the arc detection unit AS1 in the series verification state (a state in which the series electric circuit R01 is interrupted and the parallel electric circuit R02 is conductive), the series arc detection unit 72 detects a series arc in the string 2. The series arc detection unit 72 may wait for the arc detection by the arc detection unit AS1 until a series arc waiting period of a predetermined length has elapsed in the series verification state, and detect a series arc in the string 2 when an arc is detected by the arc detection unit AS1 within the series arc waiting period. As an example, after the normal state becomes the series verification state by executing the parallel extinction control after the series extinction control, the series arc detection unit 72 waits for the arc detection by the arc detection unit AS1 until the series arc waiting period has elapsed, and detects a series arc in the string 2 when an arc is detected by the arc detection unit AS1 within the series arc waiting period. A specific example of a case in which an arc is detected by the arc detection unit AS1 is when the noise level of the current detected by the current sensor 65 exceeds a predetermined level.

The series arc detection unit 72 may detect a series arc in the string 3 when an arc is detected by the arc detection unit AS2 in the second series verification state (a state in which the series electric circuit R11 is interrupted and the parallel electric circuit R12 is conductive) after the second series extinction control and the second parallel extinction control. The series arc detection unit 72 may wait for the arc detection by the arc detection unit AS2 until a predetermined length of series arc waiting period has elapsed in the second series verification state, and detect a series arc in the string 3 when an arc is detected by the arc detection unit AS2 within the series arc waiting period. As an example, after the normal state becomes the second series verification state by executing the second parallel extinction control after the second series extinction control, the series arc detection unit 72 waits for the arc detection by the arc detection unit AS2 until the series arc waiting period has elapsed, and detects a series arc in the string 3 when an arc is detected by the arc detection unit AS2 within the series arc waiting period. A specific example of when an arc is detected by the arc detection unit AS2 is when the noise level of the current detected by the current sensor 66 exceeds a predetermined level.

After the series extinction control and the parallel extinction control, the parallel arc detection unit 75 detects a parallel arc in string 2 when an arc is detected by the arc detection unit AS1 in the parallel verification state (a state in which both the series electric circuit R01 and the parallel electric circuit R02 are interrupted). The parallel arc detection unit 75 may wait for the detection of an arc by the arc detection unit AS1 until a parallel arc waiting period of a predetermined length has elapsed in the parallel verification state, and detect a parallel arc in string 2 when an arc is detected by the arc detection unit AS1 within the parallel arc waiting period. As an example, when the series arc waiting period has elapsed without an arc being detected by the arc detection unit AS1, the parallel arc detection unit 75 switches the parallel switch 62 from the on state to the off state to interrupt the parallel electric circuit R02, and then waits for the detection of an arc by the arc detection unit AS1 until the parallel arc waiting period has elapsed, and detects a parallel arc in string 2 when an arc is detected by the arc detection unit AS1 within the parallel arc waiting period. Specific examples of cases in which an arc is detected by the arc detection unit AS1 include when the noise level of the voltage detected by the voltage sensor 67 exceeds a predetermined level, when the voltage drop level detected by the voltage sensor 67 exceeds a predetermined level, etc.

When a parallel arc occurs in string 2, a current flows through string 2. However, in a parallel verification state in which both the series circuit R01 and the parallel circuit R02 are interrupted, it is difficult for the current sensor 65 to detect current noise caused by the parallel arc. On the other hand, voltage noise caused by the parallel arc can be detected by the voltage sensor 67. Therefore, the arc detection unit AS1, which includes the current sensor 65 and the voltage sensor 67, can detect a parallel arc in string 2 with higher reliability.

After the second series extinction control and the second parallel extinction control, the parallel arc detection unit 75 detects a parallel arc in the string 3 when an arc is detected by the arc detection unit AS2 in the second parallel verification state (a state in which both the series electric path R11 and the parallel electric path R12 are interrupted). The parallel arc detection unit 75 may wait for the detection of an arc by the arc detection unit AS2 until a parallel arc waiting period of a predetermined length has elapsed in the second parallel verification state, and detect a parallel arc in the string 3 when an arc is detected by the arc detection unit AS2 within the parallel arc waiting period. As an example, when the series arc waiting period has elapsed without an arc being detected by the arc detection unit AS2, the parallel arc detection unit 75 switches the parallel switch 64 from the on state to the off state to interrupt the parallel electric path R12, and then waits for the detection of an arc by the arc detection unit AS2 until the parallel arc waiting period has elapsed, and detects a parallel arc in the string 3 when an arc is detected by the arc detection unit AS2 within the parallel arc waiting period. Specific examples of cases in which an arc is detected by the arc detection unit AS2 include when the noise level of the voltage detected by the voltage sensor 68 exceeds a predetermined level, when the voltage drop level detected by the voltage sensor 68 exceeds a predetermined level, etc.

When a series arc is detected in string 2, the protection control unit 73 switches the parallel switch 62 from an on state to an off state to interrupt the parallel electric circuit R02, and when a parallel arc is detected in string 2, the protection control unit 73 switches the parallel switch 62 from an off state to an on state to make the parallel electric circuit R02 conductive. When a series arc is detected in string 3, the protection control unit 73 switches the parallel switch 64 from an on state to an off state to interrupt the parallel electric circuit R12, and when a parallel arc is detected in string 3, the protection control unit 73 switches the parallel switch 64 from an off state to an on state to make the parallel electric circuit R12 conductive.

The controller 70 may further include a recovery control unit 76. When the series arc waiting period has elapsed in the series verification state without an arc being detected by the arc detection unit AS1, and when the parallel arc waiting period has elapsed in the parallel verification state without an arc being detected by the arc detection unit AS1, the recovery control unit 76 switches the series switch 61 from the OFF state to the ON state to conduct the series circuit R01. When the series arc waiting period has elapsed in the second series verification state without an arc being detected by the arc detection unit AS2, and when the parallel arc waiting period has elapsed in the second parallel verification state without an arc being detected by the arc detection unit AS2, the recovery control unit 76 switches the series switch 63 from the OFF state to the ON state to conduct the series circuit R11.

Figure 3 is a block diagram illustrating an example of the hardware configuration of the controller 70. As shown in Figure 3, the controller 70 has a circuit 710. The circuit 710 includes a processor 711, a memory 712, a storage 713, and an input/output port 714. The storage 713 has a computer-readable storage medium, such as a non-volatile semiconductor memory. The storage 713 stores a program for causing the circuit 710 to execute the series extinction control and the parallel extinction control when an arc is detected by the arc detection unit AS1, detect the occurrence of a series arc in string 2 when an arc is detected by the arc detection unit AS1 in the series verification state after the series extinction control and the parallel extinction control, detect the occurrence of a parallel arc in string 2 when an arc is detected by the arc detection unit AS1 in the parallel verification state after the series extinction control and the parallel extinction control, and interrupt the parallel electric circuit R02 when a series arc is detected in string 2 and make the parallel electric circuit R02 conductive when a parallel arc is detected in string 2. For example, the storage 713 may store a program for configuring each functional block of the controller 70 in the circuit 710.

The memory 712 temporarily stores the programs loaded from the storage medium of the storage 713 and the results of calculations by the processor 711. The processor 711 configures each functional block of the controller 70 by executing the above programs in cooperation with the memory 712. The input/output port 714 inputs and outputs electrical signals between the series switches 61 and 63, the parallel switches 62 and 64, the current sensors 65 and 66, and the voltage sensors 67 and 68 in response to commands from the processor 711.

The controller 70 is not necessarily limited to configuring each functional block by a program. For example, each functional block of the controller 70 may be configured by a dedicated logic circuit or an ASIC (Application Specific Integrated Circuit) that integrates the dedicated logic circuit.

Figure 4 is a schematic diagram showing a modified example of the power generation system 1. In this power generation system 1, the voltage sensor 67 of the arc detection unit AS1 is replaced with a bypass circuit 67A, and the voltage sensor 68 of the arc detection unit AS2 is replaced with a bypass circuit 68A. That is, in Figure 4, the arc detection unit AS1 includes a current sensor 65 and a bypass circuit 67A, and the arc detection unit AS2 includes a current sensor 66 and a bypass circuit 68A.

The bypass circuit 67A passes an AC current through the string 2 via the current sensor 65 even when both the series circuit R01 and the parallel circuit R02 are interrupted. Therefore, even in a parallel verification state in which the series circuit R01 and the parallel circuit R02 are interrupted, the current sensor 65 can detect current noise caused by a parallel arc in the string 2. For example, the bypass circuit 67A is provided between the positive relay line 55p and the negative relay line 55n between the current sensor 65 and the series switch 61, and passes an AC current between the positive relay line 55p and the negative relay line 55n.

Similarly, the bypass circuit 68A passes AC current through the string 3 via the current sensor 66 even when both the series circuit R11 and the parallel circuit R12 are interrupted. For example, the bypass circuit 68A is provided between the positive relay line 56p and the negative relay line 56n, between the current sensor 66 and the series switch 63, and passes AC current between the positive relay line 56p and the negative relay line 56n.

As shown in FIG. 5, each of the bypass circuits 67A and 68A may include a reactor 611, a capacitor 612, and a resistor 613 connected in series to each other. This makes it possible to freely adjust the frequency band of the current noise transmitted to the current sensors 65 and 66 via the bypass circuits 67A and 68A.

Figure 6 is a schematic diagram showing another modified example of the power generation system 1. The power generation system 1A shown in Figure 6 differs from the power generation system 1 in that the power conditioning system 40A has only one converter circuit 44. The configuration of the power generation system 1A is exemplified below.

The power generation system 1A includes a power conversion system 4A instead of the power conversion system 4. The power conversion system 4A includes a power conditioning system 40A, a connection box 90, and a protection device 50A.

The power conditioning system 40A has a power conversion circuit 43A. The power conversion circuit 43A has a converter circuit 44 and an inverter circuit 46 like the power conversion circuit 43, but does not have a converter circuit 45. Therefore, the power conditioning system 40A has a positive input terminal 41p and a negative input terminal 41n corresponding to the converter circuit 44, but does not have a positive input terminal 42p and a negative input terminal 42n corresponding to the converter circuit 45.

The connection box 90 combines the DC power output by string 2 to the positive string line 23p and the negative string line 23n, and the DC power output by string 3 to the positive string line 33p and the negative string line 33n, and inputs them into the power conditioning system 40A.

For example, the connection box 90 has a positive input terminal 91p, a negative input terminal 91n, a positive input terminal 92p, a negative input terminal 92n, a positive output terminal 93p, and a negative output terminal 93n. The positive input terminal 91p is connected to the positive string line 23p via the protection device 50A, and the negative input terminal 91n is connected to the negative string line 23n via the protection device 50A. The positive input terminal 92p is connected to the positive string line 33p via the protection device 50A, and the negative input terminal 92n is connected to the negative string line 33n via the protection device 50A.

The positive output terminal 93p is connected to the positive input terminal 41p of the power conditioning system 40A by the positive trunk line 85p, and the negative output terminal 93n is connected to the negative input terminal 41n of the power conditioning system 40A by the negative trunk line 85n. The positive relay line 94p connects the positive input terminal 91p and the positive output terminal 93p in the connection box 90, and the negative relay line 94n connects the negative input terminal 91n and the negative output terminal 93n in the connection box 90. The positive relay line 95p connects the positive input terminal 92p and the positive output terminal 93p in the connection box 90, and the negative relay line 95n connects the negative input terminal 92n and the negative output terminal 93n in the connection box 90.

The junction box 90 further includes a first diode 97 and a second diode 98. The first diode 97 blocks current from string 3 to string 2. For example, the first diode 97 is provided in the positive relay line 94p and blocks current from the positive output terminal 93p to the positive input terminal 91p. The second diode 98 blocks current from string 2 to string 3. For example, the second diode 98 is provided in the positive relay line 95p and blocks reverse current from the positive output terminal 93p to the positive input terminal 92p.

In this way, when each string has a diode for preventing reverse current, it may be difficult for the current sensors 65 and 66 to detect a parallel arc even in a normal state. For example, when a parallel arc occurs in string 2, the DC voltage between the positive string line 23p and the negative string line 23n becomes lower than the DC voltage between the positive string line 33p and the negative string line 33n, so that a reverse bias voltage from the negative electrode 21n to the positive electrode 21p acts on the first diode 97. As a result, no current flows through the positive relay line 94p and the positive relay line 55p, making it difficult for the current sensor 65 provided in the positive relay line 55p to detect a parallel arc. Even in such a case, the voltage sensors 67 and 68 can detect a parallel arc. For this reason, it is more advantageous for the arc detection unit AS1 to include the current sensor 65 and the voltage sensor 67, and for the arc detection unit AS2 to include the current sensor 66 and the voltage sensor 68. In addition, the arc detection units AS1 and AS2, which include bypass circuits 67A and 68A instead of the voltage sensors 67 and 68, can also detect parallel arcs without being affected by diodes. Therefore, in the power generation system 1A shown in FIG. 6, the voltage sensors 67 and 68 can also be replaced with bypass circuits 67A and 68A.

In the power generation system 1A, it is also assumed that an arc occurs in the positive and negative main lines 85p and 85n. In a normal state, if an arc is detected by the arc detection unit AS1 and an arc is detected by the arc detection unit AS2, it is suspected that an arc occurs not in string 2 or string 3 but in the positive and negative main lines 85p and 85n. In this case, it is necessary to cut off the power supply from both string 2 and string 3 to the positive and negative main lines 85p and 85n. Therefore, when an arc is detected by the arc detection unit AS1 and an arc is detected by the arc detection unit AS2 in a normal state, the protection control unit 73 may switch the series switch 61 from the on state to the off state and switch the series switch 63 from the on state to the off state to cut off both the series circuits R01 and R11.

As shown in FIG. 7, the configuration of the connection box 90 may be incorporated into the power conditioning system 40A.

[Protection Procedures]
Next, as an example of a method for protecting the photovoltaic power generation system, a protection procedure executed by the controller 70 will be illustrated. The procedure described below is started in a normal state (a state in which the series electric circuits R01 and R11 are conductive and the parallel electric circuits R02 and R12 are interrupted).

This procedure includes: executing the series extinction control and the parallel extinction control when an arc is detected by the arc detection unit AS1; detecting the occurrence of a series arc in string 2 when an arc is detected by the arc detection unit AS1 in the series verification state after the series extinction control and the parallel extinction control; detecting the occurrence of a parallel arc in string 2 when an arc is detected by the arc detection unit AS1 in the parallel verification state after the series extinction control and the parallel extinction control; interrupting the parallel electric circuit R02 when a series arc is detected in string 2, and conducting the parallel electric circuit R02 when a parallel arc is detected in string 2.

For example, as shown in FIG. 8, the controller 70 first executes step S01. In step S01, the extinction control unit 71 waits for an arc to be detected by at least one of the arc detection units AS1 and AS2. If it is determined in step S01 that an arc has been detected by at least one of the arc detection units AS1 and AS2, the controller 70 executes step S03. In step S03, the extinction control unit 71 checks whether the level of the arc detected by the arc detection unit AS1 (e.g., the current noise level, the voltage noise level, or the voltage drop level) is greater than the level of the arc detected by the arc detection unit AS2.

If it is determined in step S03 that the arc level detected by arc detection unit AS1 is greater than the arc level detected by arc detection unit AS2, the controller 70 executes the protection procedure for string 2 shown in step S05. The specific procedure for step S05 will be described later.

If it is determined in step S01 that the arc level detected by the arc detection unit AS2 is greater than the arc level detected by the arc detection unit AS1, the controller 70 executes the protection procedure for string 3 shown in step S07. The specific procedure for step S07 will be described later.

Figure 9 is a flowchart showing the protection procedure in step S05. The arc detection process in step S05 and the arc detection process in step S07 are the same procedure, except that the target is string 2 or string 3. Therefore, the specific procedure of step S05 is illustrated, and the specific procedure of step S07 is not illustrated.

As shown in FIG. 9, the controller 70 first executes steps S11, S12, and S14. In step S11, the extinguishing control unit 71 turns off both the series switch 61 and the parallel switch 62. In step S12, the extinguishing control unit 71 switches the parallel switch 62 from the off state to the on state, thereby conducting the parallel electrical path R02.

In step S14, the series arc detection unit 72 checks whether an arc has been detected by the arc detection unit AS1. For example, the series arc detection unit 72 checks whether the noise level of the current detected by the current sensor 65 is equal to or lower than a predetermined level.

If it is determined in step S14 that the arc has not been detected by the arc detection unit AS1, the controller 70 executes step S15. In step S15, the series arc detection unit 72 checks whether the series arc waiting period has elapsed since the execution of step S12.

If it is determined in step S15 that the series arc waiting period has not elapsed, the controller 70 returns the process to step S14. Thereafter, the controller 70 repeats steps S14 and S15 until the series arc waiting period has elapsed or an arc is detected by the arc detection unit AS1.

If it is determined in step S14 that an arc has been detected by the arc detection unit AS1, the controller 70 executes step S16. In step S16, the series arc detection unit 72 detects a series arc, and the protection control unit 73 switches the parallel switch 62 from the on state to the off state to interrupt the parallel electric circuit R02. After that, the controller 70 returns the process to step S01.

If it is determined in step S15 that the series arc waiting period has elapsed, the controller 70 executes steps S21 and S23. In step S21, the parallel extinguishing control unit 74 switches the parallel switch 62 from the on state to the off state to interrupt the parallel electric circuit R02. In step S23, the parallel arc detection unit 75 checks whether an arc has been detected by the arc detection unit AS1. For example, the parallel arc detection unit 75 checks whether the noise level of the voltage detected by the voltage sensor 67 or the voltage drop level detected by the voltage sensor 67 is below a predetermined level (threshold value in the figure).

If it is determined in step S23 that the arc detection unit AS1 has not detected an arc, the controller 70 executes step S24. In step S24, the parallel arc detection unit 75 checks whether the parallel arc waiting period has elapsed since execution of step S21.

If it is determined in step S24 that the parallel arc waiting period has not elapsed, the controller 70 returns the process to step S23. Thereafter, the controller 70 repeats steps S23 and S24 until the parallel arc waiting period elapses or an arc is detected by the arc detection unit AS1.

If it is determined in step S23 that an arc has been detected by the arc detection unit AS1, the controller 70 executes step S25. In step S25, the parallel arc detection unit 75 detects a parallel arc, and the protection control unit 73 switches the parallel switch 62 from the OFF state to the ON state to make the parallel electrical path R02 conductive. After that, the controller 70 returns the process to step S01.

If it is determined in step S24 that the parallel arc waiting period has elapsed, the controller 70 executes step S26. In step S26, the recovery control unit 76 switches the series switch 61 from the OFF state to the ON state to make the series circuit R01 conductive. The controller 70 then returns the process to step S01. This completes the protection procedure for string 2. The controller 70 returns the process to step S01 after any of steps S16, S25, and S26, so that even if a series arc or parallel arc is detected, the monitoring of the arc in string 2 continues. Therefore, even if an error occurs in the detection result of a series arc or parallel arc, the protection procedure for string 2 will be executed appropriately based on the subsequent monitoring results.

As an example, when the arc detection unit AS1 detects an arc based on the voltage drop level in the voltage sensor 67, a break in the positive string line 23p or the negative string line 23n may be detected as a parallel arc. In this case, a series arc may occur at the break. In such a case, the procedure in FIG. 9 is executed again to protect the string 2 from heat generation due to the series arc.

Even if the controller 70 detects a series arc or a parallel arc and executes step S16 or step S25, the controller 70 may be configured to further execute a forced return process to return string 2 to the normal state after a predetermined time has elapsed. The controller 70 may also be configured not to execute the forced return process after the number of times the forced return process has been executed reaches a predetermined number (e.g., five times) within a predetermined return status monitoring period (e.g., 24 hours). By executing the forced return process, strings 2 and 3 can be fully utilized.

As described above, the series switches 61 and 63 may be configured such that the series switch 63 switches on and off in conjunction with the series switch 61, and the series switch 61 switches on and off in conjunction with the series switch 63. The parallel switches 62 and 64 may be configured such that the parallel switch 64 switches on and off in conjunction with the parallel switch 62, and the parallel switch 62 switches on and off in conjunction with the parallel switch 64. In this way, when the switch for string 2 and the switch for string 3 are linked, if the protection procedure of step S05 is performed for string 2, the same procedure is simultaneously performed for string 3. If the protection procedure of step S07 is performed for string 3, the same procedure is simultaneously performed for string 2.

As described above, in the power generation system 1A, it is assumed that an arc may occur in the positive pole trunk line 85p and the negative pole trunk line 85n. A protection procedure that takes this into consideration is illustrated below. As shown in FIG. 10, the controller 70 first executes the above-mentioned step S01, and then executes step S02. In step S02, the extinguishing control unit 71 checks whether the arc level detected by the arc detection unit AS1 is equivalent to the arc level detected by the arc detection unit AS2. For example, the extinguishing control unit 71 checks whether the difference between the arc level detected by the arc detection unit AS1 and the arc level detected by the arc detection unit AS2 is equal to or less than a predetermined value.

If it is determined in step S02 that the arc level detected by the arc detection unit AS1 and the arc level detected by the arc detection unit AS2 are equivalent, the controller 70 executes step S04. In step S04, the protection control unit 73 switches the series switch 61 from the on state to the off state to interrupt the series circuit R01, and switches the series switch 63 from the on state to the off state to interrupt the series circuit R11. The controller 70 then returns the process to step S01. If it is determined in step S02 that the arc level detected by the arc detection unit AS1 and the arc level detected by the arc detection unit AS2 are not equivalent, the controller 70 executes the above-mentioned protection procedure for strings 2 and 3 (steps S03, S05, and S07).

[Effects of this embodiment]
As described above, the protection device 50 includes an arc detection unit AS1 that detects an arc in the string 2 connected to the power conversion circuit 43 (load), an arc extinction control unit that executes, when an arc is detected by the arc detection unit AS1, series arc extinction control for interrupting the series electric path R01 that passes a current through the string 2 via the power conversion circuit 43 and parallel arc extinction control for conducting the parallel electric path R02 that passes a current through the string 2 without passing through the power conversion circuit 43, and a control unit that executes an arc detection control when the series electric path R01 is interrupted and the parallel electric path R02 is conducted after the series arc extinction control and the parallel arc extinction control. a series arc detection unit 72 that detects a series arc in string 2 when an arc is detected by unit AS1; a parallel arc detection unit 75 that detects a parallel arc in string 2 when an arc is detected by arc detection unit AS1 in a state in which both the series electric circuit R01 and the parallel electric circuit R02 are interrupted after the series arc extinction control and the parallel arc extinction control; and a protection control unit 73 that interrupts the parallel electric circuit R02 when a series arc is detected in string 2 and causes the parallel electric circuit R02 to be conductive when a parallel arc is detected in string 2.

If a series arc occurs in string 2, both the series circuit R01 and the parallel circuit R02 must be interrupted. On the other hand, if a parallel arc occurs in string 2, the parallel circuit R02 must be made conductive. As such, how string 2 should be protected differs depending on whether a series arc or a parallel arc has occurred, so it is important to identify with high reliability whether a series arc or a parallel arc has occurred in string 2.

In contrast, according to the protection device 50, after the series extinction control and the parallel extinction control, when the arc detection unit AS1 detects an arc in a state in which the series electric path R01 is interrupted and the parallel electric path R02 is conductive, the occurrence of a series arc in string 2 is detected. When the series electric path R01 is interrupted and the parallel electric path R02 is conductive, a parallel arc does not occur. Based on the arc detection result in such a state, a series arc can be detected with high reliability. Also, after the series extinction control and the parallel extinction control, when the arc detection unit AS1 detects an arc in a state in which both the series electric path R01 and the parallel electric path R02 are interrupted, the occurrence of a parallel arc in string 2 is detected. When both the series electric path R01 and the parallel electric path R02 are interrupted, a series arc does not occur. Based on the arc detection result in such a state, a parallel arc can be detected with high reliability.

When a series arc is detected, both the series circuit R01 and the parallel circuit R02 are interrupted, and when a parallel arc is detected, the parallel circuit R02 is made conductive. Based on the highly reliable identification result of whether it is a series arc or a parallel arc, it is possible to highly reliably protect the string 2 from heat generation due to arcs. Therefore, it is effective in highly reliably protecting the power generation system 1 from heat generation due to arcs.

The series arc detection unit 72 may wait for the arc detection unit AS1 to detect an arc until a predetermined length of series arc waiting period has elapsed with the series electric circuit R01 interrupted and the parallel electric circuit R02 conductive, and the parallel arc detection unit 75 may wait for the arc detection unit AS1 to detect an arc until a predetermined length of parallel arc waiting period has elapsed with both the series electric circuit and the parallel electric circuit interrupted. In this case, by setting a limit on the waiting time for arc detection, it is possible to quickly identify whether it is a series arc or a parallel arc.

The extinction control unit 71 executes parallel extinction control after series extinction control, the series arc detection unit 72 waits for the arc detection unit AS1 to detect an arc until a series arc standby period has elapsed after the parallel extinction control, and the parallel arc detection unit 75 may wait for the arc detection unit AS1 to detect an arc until the parallel arc standby period has elapsed after interrupting the parallel electric circuit R02 if the series arc standby period has elapsed without the arc being detected by the arc detection unit AS1. In this case, the number of times the parallel electric circuit R02 is switched between interruption and formation can be reduced, and it is possible to more efficiently identify whether the arc is a series arc or a parallel arc.

The protection device 50 may further include a recovery control unit 76 that causes the series circuit R01 to become conductive when the series arc wait period has elapsed without an arc being detected by the arc detection unit AS1 and the parallel arc wait period has elapsed without an arc being detected by the arc detection unit AS1. In this case, if a series arc is not detected during the series arc wait period and a parallel arc is not detected during the parallel arc wait period, string 2 is reconnected to the power conversion circuit 43, making it possible to effectively utilize string 2.

The protection device 50 further includes an arc detection unit AS2 that detects an arc in the string 3 connected to the power conversion circuit 43, and the extinguishing control unit 71 executes series extinguishing control and parallel extinguishing control when an arc is not detected by the arc detection unit AS2 and an arc is detected by the arc detection unit AS1, and executes a second series extinguishing control that interrupts the series electric path R11 that passes a current through the string 3 via the power conversion circuit 43 and a second parallel extinguishing control that conducts the parallel electric path R12 that passes a current through the string 3 without passing through the power conversion circuit 43 when an arc is not detected by the arc detection unit AS1 and an arc is detected by the arc detection unit AS2, and the series arc detection unit 72 executes After the second series extinction control and the second parallel extinction control, when the series electric path R11 is interrupted and the parallel electric path R12 is conductive, the arc detection unit AS2 detects an arc in string 3, and the parallel arc detection unit 75 detects a parallel arc in string 3 when the arc detection unit AS2 detects an arc in string 3 when both the second series electric path and the second parallel electric path are interrupted after the second series extinction control and the second parallel extinction control, and the protection control unit 73 may interrupt the parallel electric path R12 when the series arc in string 3 is detected, and may make the parallel electric path R12 conductive when the parallel arc in string 3 is detected. In this case, the arc in string 2 and the arc in string 3 can be distinguished with higher reliability, and the power generation system 1 can be appropriately protected from heat generation due to the arc.

When an arc is detected by the arc detection unit AS1 and an arc is detected by the arc detection unit AS2, the protection control unit 73 may shut off both the series electric circuit R01 and the series electric circuit R11. In this case, the power generation system 1 can be appropriately protected from heat generation due to an arc at a location that affects both string 2 and string 3.

The arc detection unit AS1 includes a current sensor 65 that detects the current flowing through the string 2, and a voltage sensor 67 that detects the voltage applied by the string 2 to the power conversion circuit 43. When the series electric circuit R01 is interrupted and the parallel electric circuit R02 is conductive, the arc may be detected by the current sensor 65, and when both the series electric circuit R01 and the parallel electric circuit R02 are interrupted, the arc may be detected by the voltage sensor 67. In this case, by using the current sensor 65 and the voltage sensor 67 in combination, the arc can be detected with higher reliability.

The arc detection unit AS1 may detect the voltage noise level using the voltage sensor 67. In this case, parallel arcs can be easily detected.

The arc detection unit AS1 may detect the voltage drop level using the voltage sensor 67. In this case, parallel arcs can be easily detected.

The arc detection unit AS1 may include a current sensor 65 that detects the current flowing through the string 2, and a bypass circuit 67A that passes an AC current through the string 2 via the current sensor 65 even when both the series circuit R01 and the parallel circuit R02 are interrupted. When the string 2 is connected to the power conversion circuit 43 via a diode, the effect of the diode may make it difficult for a noise current caused by a parallel arc to be transmitted to the current sensor 65. In contrast, the arc detection unit AS1 including the bypass circuit 67A makes it easier for the noise current caused by a parallel arc to be transmitted to the current sensor 65, making it possible to detect a parallel arc with higher reliability.

The bypass circuit 67A may include a reactor 611, a capacitor 612, and a resistor 613 connected in series to each other. In this case, the frequency band of the current noise transmitted to the current sensor 65 via the bypass circuit 67A is adjusted to the frequency band in which a parallel arc occurs, thereby making it possible to detect the parallel arc with higher reliability.

Although the embodiments have been described above, the present disclosure is not necessarily limited to the above-mentioned embodiments, and various modifications are possible within the scope of the gist of the present disclosure. For example, in the above, a case where the power generation system has two strings is shown, and the series arc detection process for strings 2 and 3, the parallel arc detection process for strings 2 and 3, and the protection process for the series arc or parallel arc detected in strings 2 and 3 are exemplified, but the number of strings is not limited to two. The power generation system may have at least one string, and may have three or more strings. In a power generation system with three or more strings, the protection device is configured to perform the same process for the third and subsequent strings as the series arc detection process for strings 2 and 3, the parallel arc detection process for strings 2 and 3, and the protection process for the series arc or parallel arc detected in strings 2 and 3.

2...string (solar cell string), 3...string (second solar cell string), 4, 4A...power conversion system, 43, 43A...power conversion circuit (load), 50, 50A...protection device, 65, 66...current sensor, 67, 68...voltage sensor, 67A, 68A...bypass circuit, 71...arc extinction control unit, 72...series arc detection unit, 73...protection control unit, 75...parallel arc detection unit, 76...recovery control unit, 611...reactor, 612...capacitor, 613...resistor, AS1...arc detection unit, AS2...arc detection unit (second arc detection unit), R01...series electric circuit, R02...parallel electric circuit, R11...series electric circuit (second series electric circuit), R12...parallel electric circuit (second parallel electric circuit).

Claims (13)

an arc detection unit that detects an arc in a solar cell string connected to a load;
an arc extinguishing control unit that, when an arc is detected by the arc detection unit, executes a series arc extinguishing control for interrupting a series current path through which a current flows to the solar cell string via the load, and a parallel arc extinguishing control for conducting a parallel current path through which a current flows to the solar cell string without passing through the load;
a series arc detection unit that detects a series arc in the solar cell string when the arc detection unit detects an arc in a state in which the series electric path is interrupted and the parallel electric path is conductive after the series arc extinction control and the parallel arc extinction control;
a parallel arc detection unit that detects a parallel arc in the solar cell string when an arc is detected by the arc detection unit in a state in which both the series electric path and the parallel electric path are interrupted after the series arc extinction control and the parallel arc extinction control;
a protection control unit that cuts off the parallel electric path when a series arc is detected in the solar cell string, and that turns on the parallel electric path when a parallel arc is detected in the solar cell string. the series arc detection unit waits for detection of an arc by the arc detection unit until a predetermined length of a series arc wait period has elapsed in a state in which the series electric path is interrupted and the parallel electric path is conductive;
The protection device according to claim 1 , wherein the parallel arc detection unit waits for a parallel arc waiting period of a predetermined length to elapse in a state in which both the series electric path and the parallel electric path are interrupted before detecting an arc by the arc detection unit. The extinction control unit executes the parallel extinction control after the series extinction control,
the series arc detection unit waits for the arc detection by the arc detection unit until the series arc wait period has elapsed after the parallel extinguishing control;
3. The protection device of claim 2, wherein when the series arc wait period has elapsed without an arc being detected by the arc detection unit, after interrupting the parallel electric path, the parallel arc detection unit waits until the parallel arc wait period has elapsed before detecting an arc by the arc detection unit. The protection device according to claim 3 further comprises a recovery control unit that conducts the series circuit when the series arc waiting period has elapsed without the arc being detected by the arc detection unit and the parallel arc waiting period has elapsed without the arc being detected by the arc detection unit. A second arc detection unit that detects an arc in a second solar cell string connected to the load is further provided,
The extinguishing control unit is
When an arc is not detected by the second arc detection unit and an arc is detected by the arc detection unit, the series arc extinction control and the parallel arc extinction control are executed;
when an arc is not detected by the arc detection unit and an arc is detected by the second arc detection unit, a second series arc-extinguishing control is executed to interrupt a second series electric path through which a current flows to the second solar cell string via the load, and a second parallel arc-extinguishing control is executed to conduct a second parallel electric path through which a current flows to the second solar cell string without passing through the load,
the series arc detection unit detects a series arc in the second solar cell string when the second arc detection unit detects the arc in a state in which the second series electric path is interrupted and the second parallel electric path is conductive after the second series extinction control and the second parallel extinction control;
the parallel arc detection unit detects a parallel arc in the second solar cell string when the arc is detected by the second arc detection unit in a state in which both the second series electric path and the second parallel electric path are interrupted after the second series extinction control and the second parallel extinction control;
The protection device according to any one of claims 1 to 4, wherein the protection control unit cuts off the second parallel electric path when a series arc is detected in the second solar cell string, and conducts the second parallel electric path when a parallel arc is detected in the second solar cell string. The protection device according to claim 5, wherein the protection control unit interrupts both the series electric path and the second series electric path when an arc is detected by the arc detection unit and an arc is detected by the second arc detection unit. The protection device according to any one of claims 1 to 6, wherein the arc detection unit includes a current sensor that detects the current flowing through the solar cell string and a voltage sensor that detects the voltage applied to the load by the solar cell string, and when the series electric path is interrupted and the parallel electric path is conductive, the current sensor detects an arc, and when both the series electric path and the parallel electric path are interrupted, the voltage sensor detects an arc. The protection device according to claim 7, wherein the arc detection unit detects the noise level of the voltage using the voltage sensor. The protection device according to claim 7, wherein the arc detection unit detects the voltage drop level using the voltage sensor. The protection device according to any one of claims 1 to 4, wherein the arc detection unit includes a current sensor that detects the current flowing through the solar cell string, and a bypass circuit that passes an AC current through the solar cell string via the current sensor even when both the series current path and the parallel current path are interrupted. The protection device according to claim 10, wherein the bypass circuit includes a reactor, a capacitor, and a resistor connected in series with each other. A protection device according to any one of claims 1 to 11;
a power conversion circuit as the load, the power conversion system including: the power conversion circuit converting the power output by the solar cell string into AC power. When an arc is detected by an arc detection unit in a solar cell string connected to a load, a series arc-extinguishing control is executed to interrupt a series current path through which a current flows to the solar cell string via the load, and a parallel arc-extinguishing control is executed to conduct a parallel current path through which a current flows to the solar cell string without passing through the load;
detecting a series arc in the solar cell string when the arc detection unit detects an arc in a state in which the series electric path is interrupted and the parallel electric path is conductive after the series arc extinction control and the parallel arc extinction control;
detecting a parallel arc in the solar cell string when an arc is detected by the arc detection unit in a state in which both the series electric path and the parallel electric path are interrupted after the series arc extinction control and the parallel arc extinction control;
interrupting the parallel electrical path when a series arc in the solar cell string is detected, and conducting the parallel electrical path when a parallel arc in the solar cell string is detected.

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