JP2019146297A - Operation voltage control device for solar cell - Google Patents

Abstract

To control in real time an operation voltage of a solar cell into a voltage which prevents a hot spot from being generated.SOLUTION: The operation voltage control device for a solar cell string includes: means for acquiring an I-V characteristic of the solar cell string; means for calculating a partial derivative of an output current relating to the solar cell string with respect to an output voltage on the basis of the I-V characteristic; means for determining the presence/absence of an inflection point of the partial derivative; means for determining whether the partial derivative corresponding to a voltage which is obtained by subtracting a predetermined margin from an open-circuit voltage of the solar cell string, exceeds a predetermined threshold in a case where the inflection point is present; means for setting a voltage which is not lower than a voltage corresponding to the inflection point, as the operation voltage of the solar cell string in a case where the value of the partial derivative exceeds the predetermined threshold; and control means for performing a control to follow up the operation voltage as which an output voltage of the solar cell string is set.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a technique for controlling the operating voltage of a solar cell, and more particularly to a technique for controlling the operating voltage of a solar cell to avoid a hot spot phenomenon.

  It is important to avoid the hot spot phenomenon in safely operating the photovoltaic power generation system. Here, the hot spot phenomenon means a phenomenon in which the inside of the defective cell is locally heated due to the shadow being added to the defective cell for a long time, and when this is overlooked, the temperature becomes high. The cell is deformed, and in the worst case, a fire is caused.

  In this regard, Patent Document 1 discloses a method for inspecting the presence or absence of defective cells using a projector before installing a solar cell module. However, cell defects may occur during operation of the solar cell module, and such cases cannot be dealt with by the inspection method of Patent Document 1.

  Therefore, with regard to the system in operation, hot spots are inspected manually using thermography, but such inspection methods that rely on human labor are frequently performed because they require a lot of labor and time. This is not effective as a method for avoiding failures and accidents due to the hot spot phenomenon.

Japanese Patent No. 6176939

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an operating voltage control device capable of performing real-time control of the operating voltage of a solar cell to a voltage that does not cause a hot spot.

  As a result of intensive studies on the configuration of an operating voltage control device capable of performing real-time control of the operating voltage of a solar cell to a voltage at which a hot spot does not occur, the inventor has conceived the following configuration and arrived at the present invention. .

  That is, according to the present invention, an apparatus for controlling the operating voltage of a solar cell string formed by serially connecting a plurality of solar cell modules, the means for acquiring the IV characteristics of the solar cell string, and the acquired I Means for calculating a partial derivative of the output current of the solar cell string with respect to an output voltage based on -V characteristics; and first determination means for determining the presence or absence of an inflection point of the calculated partial derivative; When there is the inflection point, a second value for determining whether a value of the partial derivative corresponding to a voltage obtained by subtracting a predetermined margin from the open voltage of the solar cell string exceeds a predetermined threshold value is determined. Determining means; means for setting a voltage not lower than a voltage corresponding to the inflection point as an operating voltage of the solar cell string when a value of the partial derivative exceeds a predetermined threshold; And control means for controlling so as to track the operating voltage the output voltage of the pond string is set, the operating voltage control device comprising is provided.

  As described above, according to the present invention, there is provided an operating voltage control device that can control the operating voltage of a solar cell in real time to a voltage that does not cause a hot spot.

The figure which shows the equivalent circuit of a solar cell string. The figure which shows the PV curve of the solar cell string to which the shadow was added. The figure which shows the structure of the solar energy power generation system by which the operating voltage control apparatus of 1st Embodiment was mounted. The flowchart of the process which the operating voltage control apparatus of 1st Embodiment performs. The figure which shows the IV characteristic which an IV characteristic acquisition part acquires. The figure which shows the partial derivative which a partial derivative calculation part calculates. The figure which shows the partial derivative which a partial derivative calculation part calculates. The figure which shows the structure of the solar energy power generation system by which the operating voltage control apparatus of 2nd Embodiment was mounted. The figure which shows the structure of the solar energy power generation system by which the abnormal condition detection apparatus of 3rd Embodiment was mounted. The flowchart of the process which an abnormal condition detection apparatus performs. The figure which shows the result of an Example. The figure which shows the thermography photograph of the solar cell module containing a defective cell.

  Hereinafter, the present invention will be described with reference to embodiments shown in the drawings, but the present invention is not limited to the embodiments shown in the drawings. In the drawings referred to below, the same reference numerals are used for common elements, and the description thereof is omitted as appropriate.

  Here, first, the basic concept of the method for controlling the operating voltage of the solar cell of the present invention will be described.

FIG. 1 shows an equivalent circuit of a solar cell string. The solar cell string shown in FIG. 1 includes N solar cell modules connected in series. A solar cell module constituting a solar cell string is composed of a plurality of cells connected in series, and a part thereof includes a cell having a crystal defect (hereinafter referred to as a defective cell). In the equivalent circuit shown in FIG. 1, a cell without a defect (hereinafter referred to as a normal cell) is regarded as a parallel circuit of a current source and a diode, while a defective cell is regarded as a parallel circuit of a current source and a diode and its reverse leakage. This is based on the current conductance _GH .

Here, consider the case where a shadow is added to a defective cell. The area ratio of the shadow is added portion as alpha (0 to 1.0), when the short-circuit current of the defective cells when the shade is not added as I _SC, the short-circuit current of the defective cells when the shadow is added is (1-α) _ISC . Here, as shown in FIG. 1A, while the output current I _PV of the solar cell string (hereinafter referred to as the string current I _PV ) does not exceed the short-circuit current (1-α) I _SC of the defective cell, the conductance Since no current flows through _GH , no hot spot is generated. Hereinafter, this state is referred to as mode 1.

On the other hand, as shown in FIG. 1 (b), the string current _{I PV} exceeds the short-circuit current _{(1-α) I SC} of the defective cell, the excess is to flow conductance _{G H.} As a result, the defective portion of the cell generates heat locally and a hot spot is generated. Hereinafter, a state in which the heat generation of the hot spot is increased with an increase in the string current I _PV and mode 2.

After that, when the current continues to flow through the conductance _GH and the negative voltage of the terminal voltage _VHS of the defective cell becomes larger than the voltage generated by the normal cell, the current is provided in parallel to the solar cell module including the defective cell. The bypass diode is forward biased. As a result, the diode of the defective cell is turned on, and the state where the heat generation at the conductance _GH is maximized is maintained. Hereinafter, this state is referred to as mode 3.

FIG. 2 shows a PV curve (bold solid line) of the solar cell string when the shadow area ratio α = 0.75, and a PV related to power consumed by the defective cell (hereinafter referred to as hot spot power). A curve (thin solid line) is also shown. As can be seen from FIG. 2, if the solar cell module is operated at the maximum power point voltage _VOP when a shadow is added to the defective cell, the hot spot power becomes maximum and is dangerous. On the other hand, if the solar cell module can be operated at the operating point X (mode 1 and mode 2 boundary) at which the hot spot power becomes zero, the hot spot can be avoided and the maximum power under that condition Can be secured.

  Based on the above-described concept, the present invention implements a method for controlling the operating voltage of a solar cell string so that the hot spot power is always zero when a shadow is added to a defective cell, and the method is executed. An operating voltage control device is disclosed.

  The basic concept of the present invention has been described above. Next, an embodiment of the operating voltage control apparatus of the present invention will be described.

(First embodiment)
FIG. 3 shows a system configuration of a photovoltaic power generation system 1000 on which the solar cell operating voltage control apparatus 100 according to the first embodiment of the present invention is mounted. As shown in FIG. 3, the photovoltaic power generation system 1000 includes a solar cell string (hereinafter sometimes referred to as a PV string) 50, a voltmeter 52 that measures an output voltage of the PV string 50, and an output of the PV string 50. An ammeter 53 for detecting current and a power conditioner (PCS) 30 are included. The PCS 30 includes a DC-DC converter 20 including an inductor 22, a switch element 23, a diode 24, and a smoothing capacitor 25; The operating voltage control apparatus 100 of this embodiment is mounted.

  The operating voltage control apparatus 100 of the present embodiment performs a predetermined calculation based on the voltage value and the current value input from the voltmeter 52 and the ammeter 53, and turns on / off the switch element 23 based on the calculation result. Is a device for controlling the operating voltage of the PV string 50 by performing PWM control, and includes an IV characteristic acquisition unit 12, a partial derivative calculation unit 13, a shadow occurrence determination unit 14, and a hot spot occurrence determination unit 15. And an operation voltage setting unit 16, an operation voltage control unit 17, and an MPPT control unit 18.

  The IV characteristic acquisition unit 12 is means for acquiring the IV characteristic of the PV string 50 based on the detection values input from the voltmeter 52 and the ammeter 53.

The partial derivative calculation unit 13 is a means for calculating a partial derivative of the output current I _PV related to the PV string 50 with respect to the output voltage V _PV based on the IV characteristic acquired by the IV characteristic acquisition unit 12. .

  The shadow occurrence determination unit 14 is means for determining the presence or absence of an inflection point of the partial derivative calculated by the partial derivative calculation unit 13.

When there is an inflection point in the partial derivative, the hot spot occurrence determination unit 15 sets the value of the partial derivative corresponding to the voltage obtained by subtracting a predetermined margin from the open voltage V _OCS of the PV string 50 to a predetermined threshold value. It is a means for determining whether or not it exceeds.

  The operating voltage setting unit 16 is means for setting a voltage corresponding to the inflection point as the operating voltage of the PV string 50 when the value of the partial derivative exceeds a predetermined threshold value.

  The operating voltage control unit 17 is means for controlling the output voltage of the PV string 50 to track the set operating voltage.

  The MPPT control unit 18 is means for tracking and controlling the maximum power operating point by the hill-climbing method based on the detection values input from the voltmeter 52 and the ammeter 53.

  Note that the above-described means constituting the operating voltage control apparatus 100 can be realized by hardware, software, or a combination thereof, and when part or all of the above-described means is realized by software, the operating voltage control apparatus A computer mounted on the computer 100 functions as the above-described units by executing a predetermined program.

  The functional configuration of the operating voltage control apparatus 100 according to the present embodiment has been described above. Next, processing executed by the operating voltage control apparatus 100 will be described. In the following description, FIG. 3 will be referred to as appropriate.

  The operating voltage control apparatus 100 according to the present embodiment periodically performs a process for setting an operating voltage (hereinafter referred to as a safe operating voltage) at which the PV string 50 can safely operate at a predetermined cycle. The safe operating voltage setting process will be described below based on the flowchart shown in FIG.

  First, in step 101, the IV characteristic acquisition unit 12 monitors the arrival of a preset scan cycle (step 101, No), and detects the arrival of the scan cycle (step 101, Yes). Proceed to

In subsequent step 102, the IV characteristic acquisition unit 12 scans the PV string 50 and acquires the IV characteristic (current-voltage curve) of the PV string 50. Specifically, the output voltage V detected by the voltmeter 52 and the ammeter 53 during that time is changed from the open state to the short-circuited state between the negative and positive terminals of the PV string 50 by the on / off control of the switch element 23. _The IV characteristic is derived based on the _PV and the output current I _PV .

  5A to 5C show the IV characteristics acquired in step 102. FIG. Here, FIG. 5A shows an IV characteristic obtained when a shadow is not added to a PV string without a defective cell (hereinafter referred to as a normal string), and FIG. FIG. 5C illustrates IV characteristics obtained when a shadow is added to a normal string. FIG. 5C illustrates a case where a shadow is added to a defective cell of a PV string including a defective cell (hereinafter referred to as a defective string). The IV characteristics acquired when the As shown in FIG. 5C, in the IV curve in the case where a shadow is added to the defective cell, the portion corresponding to the above-described mode 2 appears as a straight line having a negative slope.

In subsequent step 103, the partial derivative calculation unit 13 calculates a partial derivative of the string current I _PV of the PV string 50 with respect to the string voltage V _PV based on the IV characteristic acquired in step 102.

  In subsequent step 104, the shadow occurrence determination unit 14 determines whether or not the partial derivative acquired in step 103 has an inflection point. As a result, when there is an inflection point (step 104, Yes), the process proceeds to step 105, and when there is no inflection point (step 104, No), the process proceeds to step 108, and the hot spot flag is set. Turn off.

  FIG. 6A shows the partial derivative obtained in step 103 when no shadow is added to the normal string. In this case, since the inflection point does not exist in the partial derivative, the hot spot flag is set to OFF.

  FIG. 6B shows a partial derivative obtained when a shadow is added to a normal string, and FIG. 6C is obtained when a shadow is added to a defect cell of the defect string. Indicates the partial derivative. As shown in FIGS. 6B and 6C, in this case, since there exists an inflection point in any partial derivative, the process proceeds to step 105.

In step 105, the hot spot occurrence determination unit 15, the value of partial derivatives corresponding to the voltage _{V GH} from the open-circuit voltage _{V OCS} by subtracting a predetermined margin M of PV strings 50 | ∂I / ∂V | is zero Determine if it has exceeded. Note that this zero is an example of a threshold value and is not limited to this value, and determination may be made using a value obtained by adding a predetermined margin to zero as a threshold value. Further, the margin M here can be set to a value corresponding to ½ of the nominal open circuit voltage V _OC of one PV module constituting the PV string 50, for example.

  As a result of the determination in step 105, if it does not exceed zero (step 105, No), the process proceeds to step 108, the hot spot flag is turned off, and if it exceeds zero (step 105, Yes), The process proceeds to step 106 to set the hot spot flag to ON.

If you have a shadow is added to the normal strings, as shown in FIG. 7 (a), the value of partial derivatives corresponding to the voltage V _GH | ∂I / ∂V | because does not exceed zero, hotspots flag Is set to OFF. On the other hand, if it is added shadow defective cells defective strings, as shown in FIG. 7 (b), the value of partial derivatives corresponding to the voltage V _GH | ∂I / ∂V | since exceeds zero The hot spot flag is set to ON.

When the hot spot flag is set to ON, in the subsequent step 107, the operating voltage setting unit 16 performs the safe operation using the voltage V _X corresponding to the inflection point determined in the previous step 104 as the operating voltage of the PV string 50. Set to voltage. Here, as shown in FIG. 7B, when two inflection points exist in the partial derivative, the higher one of the two corresponding voltages (in this case, corresponding to the inflection point B). Voltage V _X ) is set to a safe operating voltage. The safe operating voltage V _X set at this time corresponds to the voltage V _X corresponding to the operating point X shown in FIG.

  As described above, in the present embodiment, the hot spot flag is set to ON or OFF and the hot spot flag is set to ON by the safe operating voltage setting process that is periodically executed during the operation of the system. If so, a safe operating voltage is set.

On the other hand, the operating voltage control unit 17 is activated only when the hot spot flag is set to ON, so that the output voltage V _PV of the PV string 50 follows the set safe operating voltage V _X. On / off control (PWM control) of the switch element 23 is performed.

On the other hand, the MPPT control unit 18 is activated only when the hot spot flag is set to OFF, and the output power P _PV of the PV string 50 is set to the maximum power operating point P _max of the PV string 50 by the hill-climbing method. On / off control (PWM control) of the switch element 23 is performed so as to follow.

  As described above, according to the present embodiment, a situation where a hot spot can occur during operation of the photovoltaic power generation system 1000 (that is, a situation where a shadow is added to a defective cell) has been reached. However, it is possible to safely supply the maximum power under the conditions while avoiding the occurrence of hot spots until a measure such as replacing a defective module (panel) is performed.

In the present embodiment, when only avoiding hot spots is considered, a voltage not lower than the voltage V _X , that is, an arbitrary voltage between the open voltage V _OCS of the PV string 50 and the voltage V _X is set as the safe operating voltage. Can be set as

In the modification of the present embodiment, the function of the MPPT control unit 18 described above can be replaced with the operating voltage control unit 17. In this case, the operating voltage control unit 17 acquires the maximum power point voltage V _OP corresponding to the maximum power operating point P _max of the PV string 50 based on the IV characteristic acquired in the previous step 101, and the hot spot When the flag is set to OFF, on / off control (PWM control) of the switch element 23 is performed so that the output voltage V _PV of the PV string 50 follows the acquired maximum power point voltage V _OP. .

(Second Embodiment)
FIG. 8 shows a system configuration of a photovoltaic power generation system 2000 in which the operating voltage control apparatus 200 according to the second embodiment of the present invention is mounted. The operating voltage control apparatus 200 according to the present embodiment is an apparatus configured to be additionally provided with respect to the existing PCS 40. The operating voltage control apparatus 100 according to the first embodiment is different from the MPPT control unit 18. And that the operating voltage setting unit 16 is configured to transmit a signal indicating the ON / OFF state of the hot spot flag (hereinafter referred to as a hot spot flag signal) to the PCS 40. Other configurations are common.

In the present embodiment, when the hot spot flag is set to ON, the operating voltage control device 200 transmits a hot spot flag signal (ON) to the PCS 40. In response to this, the MPPT control unit 26 on the PCS 40 side interrupts the MPPT control, while the operating voltage control unit 17 causes the output voltage V _PV of the PV string 50 to follow the set safe operating voltage V _X. In addition, on / off control (PWM control) of the switch element 23 is performed.

When the hot spot flag is set to OFF, the operating voltage control unit 17 interrupts the PMW control, while the operating voltage control device 200 transmits a hot spot flag signal (OFF) to the PCS 40. In response to this, the MPPT control unit 26 on the PCS 40 side turns on / off the switch element 23 so that the output power P _PV of the PV string 50 follows the maximum power operating point P _max of the PV string 50 by the hill-climbing method. Off control (PWM control) is performed.

  As described above, the operating voltage control apparatus 200 of the present embodiment can be additionally provided for an existing PCS for the purpose of avoiding hot spots.

  As mentioned above, although this invention has been demonstrated based on 1st and 2nd embodiment, this invention can be further considered as the abnormal condition detection method of a solar cell, and an apparatus which performs it. Hereinafter, a third embodiment according to the abnormal state detection device will be described.

(Third embodiment)
FIG. 9 shows a system configuration of a photovoltaic power generation system 3000 on which the abnormal state detection device 300 according to the third embodiment of the present invention is mounted. The abnormal state detection device 300 according to the present embodiment is a device configured to be additionally provided with respect to the existing PCS 40. The operation voltage control device 200 according to the second embodiment is different from the operation voltage setting unit. 16 and the operating voltage control unit 17 are different, and the remaining configuration is common.

  Hereafter, the content of the process which the abnormal condition detection apparatus 300 of this embodiment performs is demonstrated based on the flowchart shown in FIG. Note that the processing in steps 101 to 104 and step 105 is the same as that described in FIG.

In the present embodiment, in response to the arrival of a preset scan cycle (step 101, Yes), the IV characteristic acquisition unit 12 acquires the IV characteristic of the PV string 50 (step 102), The function calculation unit 13 calculates a partial derivative of the string current I _PV of the PV string 50 with respect to the string voltage V _PV based on the acquired IV characteristics (step 103).

  In response to this, in this embodiment, the shadow occurrence determination unit 14 determines whether there is an inflection point in the partial derivative (step 104), and adds a shadow to the PV module according to the determination result. It is detected whether or not it is in a state, and a state signal 1 indicating each state is output to the outside. Specifically, when there is an inflection point (step 104, Yes), an ON signal of the state signal 1 (a signal indicating that a shadow is added to the PV module) is output (step 120), and the inflection point is output. If there is no point (step 104, No), an OFF signal of state signal 1 (a signal indicating a state where no shadow is added to the PV module) is output (step 122).

In response to the fact that the shadow generation determination unit 14 has output the ON signal of the state signal 1 (step 120), in this embodiment, the hot spot generation determination unit 15 determines the value of the partial derivative corresponding to the voltage V _GH | It is determined whether or not I / ∂V | exceeds zero (step 105), and according to the determination result, whether or not a hot spot can be generated is detected, and each state is indicated. Signal 2 is output to the outside. Specifically, if it exceeds zero (step 105, Yes), an ON signal of state signal 2 (a signal indicating a state where a hot spot can occur) is output (step 121), and does not exceed zero. If this is the case (step 105, No), an OFF signal of state signal 2 (a signal indicating a state where no hot spot is generated) is output (step 123).

  In the present embodiment, as the output destination of the state signals 1 and 2 described above, an arbitrary device that uses the state signals 1 and 2 as a control signal, such as an alarm device for alarming a system abnormality or a monitoring device for monitoring the system state. Can be envisaged.

  As described above, according to the present embodiment, it is possible to detect in real time an abnormality (shadow or hot spot) that occurs during the operation of the solar power generation system 3000 and notify the outside of the abnormality. .

  As described above, the present invention has been described with the embodiment. However, the present invention is not limited to the above-described embodiment, and within the scope of other embodiments that can be considered by those skilled in the art, such as a combination of the above-described embodiments. As long as the operations and effects of the present invention are exhibited, they are included in the scope of the present invention.

  Hereinafter, the operating voltage control apparatus of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples described later.

  The operating voltage control device of the present invention was mounted on a PV string in which a normal PV module (50 W) and a PV module (50 W) including a defective cell were connected in series, and a verification experiment was performed according to the following procedure. In this experiment, as an example, the PV module was irradiated with light with a shadow (α = 0.75) added to the defective cell, and the above-described operation voltage setting process was executed at intervals of 4 seconds. On the other hand, as a comparative example, light was applied to the PV string under the same conditions as in the example, and only MPPT control was executed.

  FIG. 11A shows, as a result of the example, a PV string PV curve (thick solid line) and a PV curve (thin solid line) related to hot spot power of a defective cell. As shown in FIG. 11A, in the example, the maximum power point voltage was about 20V, while the safe operating voltage was about 37V.

  On the other hand, FIG. 11B shows an operation waveform (current: thick solid line, voltage: thin solid line) of the PV string as a result of the example. As shown in FIG. 11B, in the embodiment, the operating voltage once settled to the maximum power point voltage (about 20 V) by the MPPT control. The voltage shifted from the maximum power point voltage (about 20V) to the safe operating voltage (about 37V).

  Fig.12 (a) shows the thermography photograph of the PV module containing the defective cell in a comparative example, and FIG.12 (b) shows the thermography photograph of the PV module containing the defective cell in an Example. In the comparative example in which only the MPPT control is executed, as shown in FIG. 12A, a hot spot is generated in the defective cell, and the temperature of the hot spot point is the upper limit (50 ° C.) of the cell operating temperature defined by the JIS standard. The temperature rose to about 101.9 ° C. over ± 10 ° C.). On the other hand, in the example, as shown in FIG. 12B, no hot spot was generated, and the temperature of the cell was maintained at 29.8 ° C. (normal temperature).

DESCRIPTION OF SYMBOLS 12 ... IV characteristic acquisition part 13 ... Partial derivative calculation part 14 ... Shadow generation | occurrence | production determination part 15 ... Hot spot generation | occurrence | production determination part 16 ... Operating voltage setting part 17 ... Operating voltage control part 18 ... MPPT control part 20 ... DC-DC Converter 22 ... Inductor 23 ... Switch element 24 ... Diode 25 ... Smoothing capacitor 26 ... MPPT controller 50 ... PV string 52 ... Voltmeter 53 ... Ammeter 100, 200 ... Operating voltage controller 300 ... Abnormal state detector 1000, 2000, 3000 ... Solar power generation system

Claims (8)

A device for controlling the operating voltage of a solar cell string formed by a plurality of solar cell modules in series,
Means for obtaining the IV characteristics of the solar cell string;
Means for calculating a partial derivative of the output current of the solar cell string with respect to the output voltage based on the acquired IV characteristics;
First determination means for determining the presence or absence of an inflection point of the calculated partial derivative;
When there is the inflection point, a second value for determining whether a value of the partial derivative corresponding to a voltage obtained by subtracting a predetermined margin from the open voltage of the solar cell string exceeds a predetermined threshold value is determined. A determination means;
Means for setting, as an operating voltage of the solar cell string, a voltage not lower than a voltage corresponding to the inflection point when a value of the partial derivative exceeds a predetermined threshold;
Control means for controlling the output voltage of the solar cell string to track the set operating voltage;
An operating voltage control device. The operating voltage controller is
Means for performing MPPT control so that the output power of the solar cell string tracks the maximum power operating point by a hill-climbing method when it is determined that the value of the partial derivative does not exceed the predetermined threshold;
The operating voltage control apparatus according to claim 1. The control means includes
When it is determined that the value of the partial derivative does not exceed the predetermined threshold value, the maximum power point voltage of the solar cell string is obtained based on the IV characteristics, and the output voltage of the solar cell string is Control to track the maximum power point voltage;
The operating voltage control apparatus according to claim 1. The margin is a value corresponding to 1/2 of the open circuit voltage of the solar cell module.
The operating voltage control apparatus as described in any one of Claims 1-3. A device for detecting an abnormal state of a solar cell string in which a plurality of solar cell modules are connected in series,
Means for obtaining the IV characteristics of the solar cell string;
Means for calculating a partial derivative of the output current of the solar cell string with respect to the output voltage based on the acquired IV characteristics;
A shadow occurrence determining means for determining the presence or absence of an inflection point of the calculated partial derivative;
Generation of a hot spot that determines whether the value of the partial derivative corresponding to a voltage obtained by subtracting a predetermined margin from the open voltage of the solar cell string exceeds a predetermined threshold when the inflection point is present A determination means;
Including
The shadow occurrence determining means is
When there is the inflection point, a first state signal indicating a state in which a shadow is added to the solar cell module is output to the outside.
The hot spot occurrence determination means includes
When the value of the partial derivative exceeds a predetermined threshold, a second state signal indicating a state where a hot spot can occur is output to the outside.
Abnormal state detection device. A method for controlling an operating voltage of a solar cell string in which a plurality of solar cell modules are connected in series,
Obtaining the IV characteristics of the solar cell string;
Calculating a partial derivative of the output current of the solar cell string with respect to the output voltage based on the acquired IV characteristics;
Determining the presence or absence of an inflection point of the calculated partial derivative;
Determining whether the value of the partial derivative corresponding to the voltage obtained by subtracting a predetermined margin from the open voltage of the solar cell string exceeds a predetermined threshold when there is the inflection point;
When the value of the partial derivative exceeds a predetermined threshold, setting a voltage not lower than the voltage corresponding to the inflection point as the operating voltage of the solar cell string;
Controlling the output voltage of the solar cell string to track the set operating voltage;
Including methods. A method for detecting an abnormal state of a solar cell string in which a plurality of solar cell modules are connected in series,
Obtaining the IV characteristics of the solar cell string;
Calculating a partial derivative of the output current of the solar cell string with respect to the output voltage based on the acquired IV characteristics;
Determining the presence or absence of the inflection point of the calculated partial derivative, and when there is an inflection point, detecting that a shadow is added to the solar cell module;
When there is the inflection point, it is determined whether or not a value of the partial derivative corresponding to a voltage obtained by subtracting a predetermined margin from the open circuit voltage of the solar cell string exceeds a predetermined threshold value. Detecting that a hot spot may occur if the value of the derivative exceeds a predetermined threshold;
Including methods.   The program for making a computer perform each step of the method of Claim 6 or 7.