JP2015103699A - Abnormality detection method of solar cell string, abnormality detection device and photovoltaic power generation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality detection method capable of detecting abnormality of a solar cell string accurately.SOLUTION: The controller 6 of a photovoltaic power generation device 1 monitors the midpoint potential V (m) of each solar cell string 2 (m), and detects the occurrence of abnormality in a solar cell module 7 (m, n) based on the midpoint potential V (m). Upon occurrence of abnormality in one of a plurality of solar cell modules connected in series, the voltage across that solar cell module becomes lower than the voltages across other solar cell modules. The midpoint potential V (m) of the solar cell string is shifted significantly to the side of polarity connected with the solar cell module where the abnormality has occurred. Abnormality of a solar cell module can be detected more accurately than when the terminal current is monitored.

Description

  The present invention relates to a solar power generation device, and more particularly, to a solar cell string abnormality detection method and an abnormality detection device for detecting abnormalities such as inability to generate power and generation failure of each solar cell string.

  In general, a solar power generation apparatus converts DC power generated by each of a plurality of sets of solar cell strings into AC power by a power conditioner and supplies the AC power to a load side. Each of the solar cell strings has a configuration in which a plurality of solar cell modules (solar panels) are connected in series between a positive terminal and a negative terminal. Each solar cell module is provided with a bypass circuit composed of a bypass diode, and a series circuit of solar cell modules is maintained through the bypass circuit even when some of the solar cell modules fail.

  In a solar power generation apparatus having a large number of solar cell modules, abnormalities such as power generation failure, inability to generate power, and ground fault may occur in the solar cell module due to deterioration over time. In that case, the solar cell module Repair or replacement is required. It is difficult to detect the occurrence of abnormality in the solar cell module simply by monitoring the DC voltage and DC current on the input side of the power conditioner. Therefore, each terminal current and terminal voltage of the solar cell string are monitored, and a failure or abnormality is detected for each solar cell string.

  In the monitoring apparatus described in Patent Document 1, the current value of each solar cell string is measured, or the power value is calculated by measuring the current value and the voltage value, and the measured current value or the calculated power value is calculated for a certain period. It accumulates over the whole, and the occurrence of power generation failure or the like of each solar cell string is detected based on the calculated accumulated value. Moreover, in the monitoring apparatus of patent document 2, the positive side terminal current and the negative side terminal current are measured in each of the solar cell strings, and whether or not a ground fault has occurred in the solar cell string based on the difference between these currents. Detected.

JP 2011-77477 A JP 2011-71346 A

  When monitoring the terminal current of each solar cell string, the terminal current of the solar cell string in which an abnormality has occurred is compared with the terminal current of a solar cell string that is normally generating power to determine whether there is an abnormality. Each solar cell string is connected in parallel to a power conditioner, and maximum power point tracking (MPPT) control is performed by the power conditioner. Therefore, the terminal current value of the solar cell string in which an abnormality has occurred is only slightly reduced as compared with the terminal current value of a normal solar cell string. For this reason, as proposed in Patent Document 1, it is necessary to integrate the current value over a certain period and detect the occurrence of abnormality based on the integrated value.

Of course, if each terminal voltage of a solar cell module is monitored in each solar cell string, those abnormalities can be detected reliably. However, in the case of a solar power generation device including a large number of solar cell modules, monitoring the terminal voltage of each solar cell module causes a significant increase in manufacturing cost, and is not practical.

  On the other hand, the conventional ground fault detection method for solar cell strings is based on the difference between the terminal currents on both sides of each solar cell string, as described in Patent Document 2. However, depending on the ground fault state of the solar cell string, there may be no difference between the terminal current values. In this case, there is a problem that it is not possible to detect that a ground fault has occurred.

  In view of these points, an object of the present invention is to provide an abnormality detection method and an abnormality detection device capable of accurately detecting an abnormality in a solar cell string with an inexpensive configuration, and a solar power generation apparatus including the abnormality detection device. Is to provide.

  In order to solve the above-described problem, the present invention provides an abnormality detection method for a solar cell string including a plurality of solar cell modules connected in series between a positive terminal and a negative terminal. The midpoint potential, which is the potential at the midpoint position between the positive terminal and the negative terminal, is monitored, and based on the midpoint potential, whether or not an abnormality has occurred in any of the solar cell modules It is characterized by detecting.

  The midpoint potential of the solar cell string is determined by the power generation characteristics of each solar cell module constituting the solar cell string. For example, when the power generation characteristics of the solar cell modules are the same, the midpoint potential is 0 volts. In a solar cell string, when an abnormality (power generation failure, power generation failure, etc.) occurs in one of a plurality of solar cell modules connected in series, the bypass diode of the abnormality occurrence part is turned on, and the voltage across the two Only becomes lower than the voltage across the other solar cell modules. As a result, the midpoint potential of the solar cell string shifts to the side where the abnormal solar cell module is connected. For example, when the solar cell module in an abnormal state is located between the midpoint position and the positive terminal of the solar cell string, the midpoint potential shifts to the positive side. Therefore, the abnormality of the solar cell module can be detected based on the midpoint potential.

  When the abnormality occurs in the solar cell module, the variation rate of the midpoint potential is larger than the variation rate of the terminal current value of the solar cell string, so the S / N ratio is high, and the abnormality of the solar cell module can be detected with high accuracy. . In addition, the midpoint potential can be measured at a lower cost than when the terminal current is measured. Furthermore, an abnormal state can be detected in a shorter time than when terminal currents are integrated over a certain period.

  Further, as described above, the midpoint potential shifts to the polarity side where the solar cell module in which the abnormality has occurred is located. Therefore, when the shift direction of the midpoint potential is the positive side, it can be seen that an abnormality has occurred in any of the solar cell modules arranged between the midpoint position and the positive side terminal in the solar cell string. In the opposite case, it can be seen that an abnormality has occurred in any of the solar cell modules arranged between the midpoint position and the negative terminal. Compared to simply detecting the presence or absence of an abnormality in the solar cell string, it is convenient because the solar cell module in which an abnormality has occurred can be identified more easily and quickly.

Further, when a ground fault occurs at the midpoint position in the solar cell string and the ground fault potential is at the circuit ground potential level, no offset or fluctuation is observed in the midpoint potential. Therefore, it is possible to detect that a ground fault with respect to the circuit ground potential has occurred at the midpoint position of the solar cell string based on the midpoint potential. In the case of a two-point ground fault in which such a ground fault occurs and then a ground fault occurs at another position of the solar cell string, each solar cell module connected between the two point ground faults Excessive current will continue to flow and these areas may generate heat and cause a fire. According to the present invention, such adverse effects can be prevented in advance.

  Next, the abnormality detection device of the present invention that detects an abnormality of the solar cell string using the above method is a potential at a midpoint position between the positive terminal and the negative terminal of the solar cell string. A detection unit that detects a point potential; and a determination unit that determines whether or not an abnormality has occurred in any of the solar cell modules based on the midpoint potential detected by the detection unit. It is characterized by.

  Moreover, the solar power generation device of the present invention includes a plurality of sets of solar cell strings, a power conditioner that converts each generated power of the solar cell strings connected in parallel to AC power, and each of the solar cell strings. It has the abnormality detection apparatus of the said structure which detects whether abnormality has generate | occur | produced, It is characterized by the above-mentioned.

It is a schematic block diagram which shows the whole structure of the solar power generation device to which this invention is applied. (A) And (b) is explanatory drawing which shows the change of the midpoint electric potential when abnormality generate | occur | produces in a solar cell string. (A) And (b) is explanatory drawing for demonstrating the predominance of the abnormality detection method using a midpoint potential. It is explanatory drawing which shows the shift direction of the midpoint electric potential with respect to an abnormality generation position.

  Below, with reference to drawings, embodiment of the solar power generation device to which this invention is applied is described.

  FIG. 1 is a schematic configuration diagram showing the overall configuration of the photovoltaic power generation apparatus according to the present embodiment. The basic configuration of the solar power generation device 1 is general, and the solar cell array 3 including one or more sets of solar cell strings 2 (m) (m = 1, 2, 3,...), Connection Each of the solar cell strings 2 (m) is provided with a power conditioner 5 connected in parallel to the DC input port side via a box 4 and a controller 6 mainly composed of a computer.

  Each solar cell string 2 (m) has a plurality of solar cell modules 7 (m, n) (n = 2, 2) connected in series between its positive terminal 2a (m) and negative terminal 2b (m). 3, 4 ...). The DC power generated by the solar cell string 2 (m) is supplied to the power conditioner 5 through the connection box 4, and after being changed to AC power, is output from the AC output port to the load side. Each of the solar cell strings 2 (m) detects a midpoint potential V (m) that is a potential at the midpoint position 8 (m) between the positive terminal 2a (m) and the negative terminal 2b (m). A detecting unit 9 (m) is attached.

  The controller 6 includes a control unit 6a, a storage unit 6b, and the like, and is supplied with a midpoint potential V (m) and the like via the I / O port 6c. In addition, peripheral devices such as the operation input unit 11 and the display unit 12 are connected via the I / O ports 6d and 6e. The controller 6 functions as an abnormality detection device that monitors whether or not an abnormality has occurred in each solar cell string 2 (m) based on the midpoint potential V (m) detected by each detection unit 9 (m). .

In the illustrated solar cell string 2 (m), for example, ten solar cell modules 7 (m, 1) to 7 (m, 10) are connected in series. In this case, the connection point between the fifth solar cell module 7 (m, 5) and the sixth solar cell module 7 (m, 6) counted from one terminal, for example, the positive terminal 2a (m). Is the midpoint position 8 (m). The detector 9 (m) detects a potential difference between the midpoint position 8 (m) and the circuit ground potential (GND potential). In many non-insulated power conditioners, the GND potential is close to zero.

  Here, the inter-terminal potential Vo on the DC input side of the power conditioner 5 is determined by the overall power generation characteristics and incident light conditions of the solar cell array 3. In many cases, the potential is symmetric with respect to the GND potential. For example, when Vo is 600 V, the positive terminal side is +300 V and the negative terminal side is −300 V with respect to the GND potential. On the other hand, the midpoint potential V (m) of each solar cell string 2 (m) is different from the inter-terminal potential Vo of the power conditioner 5, and each of the solar cell strings 2 (m) Is an independent value for.

  FIG. 2A is an explanatory diagram showing a shift of the midpoint potential V (m) when an abnormality occurs in the solar cell string, and FIG. 2B is a voltage distribution in the solar cell module where the abnormality occurs. It is explanatory drawing which shows a state. With reference to these figures, the shift of the midpoint potential V (m) of the solar cell string 2 (m) where abnormality has occurred will be described based on the midpoint potential V (m).

  First, as shown in FIG. 2 (a), in the second solar cell string 2 (2) (m = 2), the second solar cell module 7 (2, 2) counted from the positive terminal 2a (2). 2) It is assumed that an abnormality (power generation failure) has occurred in (n = 2). In this case, the value of the inter-terminal potential Vo on the input side of the power conditioner 5 is a normal solar cell string 2 (1), 2 (3) to 2 (m), and a solar cell string 2 in which an abnormality has occurred. Since (2) is connected in parallel, there is no significant change. Further, no significant changes are observed in the midpoint potentials V (1) and V (3) to V (m) of the normal solar cell strings 2 (1) and 2 (3) to 2 (m). In contrast, the value of the midpoint potential V (2) of the solar cell string 2 (2) where the abnormality has occurred is greatly shifted.

  This point will be described with reference to FIG. In the solar cell module 7 (2, 2) of the solar cell string 2 (2) in which an abnormality has occurred, an abnormality occurs in one of the plurality of solar cells 13 connected in series, and one bypass It is assumed that the diode Di is turned on. Each of the solar cells 13 is composed of a plurality of circuit blocks called clusters that are separated by a bypass diode Di. Since the both-end potential of the cluster 14 in which an abnormality has occurred is short-circuited via the bypass diode Di, it becomes extremely lower than the both-end potential of a normal cluster. For example, if the both-end potential of each cluster is 10V, the both-end voltage of the cluster 14 where the abnormality has occurred decreases to about 1V. This voltage drop appears almost as it is at the midpoint potential V (2).

  That is, each of the normal solar cell modules 7 (2,1) and 7 (2,3) -7 (2, n) in the solar cell string 2 (2) in which an abnormality has occurred is connected to the normal solar cell string 2 (1 ) Since the voltages are common to 2 (3) to 2 (m), the terminal voltage of the solar cell string 2 (2) itself in which the abnormality has occurred is not greatly changed although the terminal voltage thereof increases. . On the other hand, in the solar cell string 2 (2) in which an abnormality has occurred, the midpoint potential V (2) is largely shifted due to a short circuit of the bypass diode Di. In the illustrated example, the solar cell module 7 (2, 2) in which an abnormality has occurred is located on the positive terminal 2a (2) side with the midpoint position 8 (2) as a boundary. Therefore, the midpoint potential V (2) is largely shifted to the positive side in response to the change in the voltage across the cluster 14 in the solar cell module 7 (2, 2) where the abnormality has occurred. The shift amount of the midpoint potential V (m) is generally about several volts, and the occurrence of abnormality can be easily determined.

Here, the sensitivity of the midpoint potential V (m) will be described with reference to FIG. Fig.3 (a) is explanatory drawing which shows the example of the IV characteristic curve at the time of the light irradiation of a solar cell module. A characteristic curve C1 shows an IV characteristic curve during light irradiation in a normal solar cell module. A point A1 on the characteristic curve C1 indicates a maximum power point (MPP) by the power conditioner 5, and a point A2 indicates an operating point of a normal solar cell module in the solar cell string where an abnormality has occurred. On the other hand, the characteristic curve C2 shows the IV characteristic curve of the solar cell module in which an abnormality has occurred, and the point B on the characteristic curve C2 shows the operating point of the solar cell module in which an abnormality has occurred. This operating point has an extremely small voltage value compared to the operating point of a normal solar cell module.

  In the solar cell string in which an abnormality has occurred, the voltage difference ΔV between the operating point A2 and the operating point B is observed as the voltage shift amount of the midpoint potential V (m). The ratio of the current shift amount represented by the current difference ΔI between the operating point A2 and the operating point B is extremely small as compared with the ratio of the voltage shift amount, and decreases as the number of solar cell strings arranged in the array increases. Therefore, the method for detecting a solar cell string including a solar cell module in which an abnormality has occurred based on the shift amount of the midpoint potential V (m) is a method for detecting an abnormality based on the shift amount of the terminal current of the solar cell string. In comparison, the sensitivity to occurrence of abnormality is high, and abnormality can be detected with high accuracy.

  FIG. 3B is an explanatory diagram illustrating an example of a change in the IV characteristic curve accompanying an increase or decrease in the amount of incident light. The characteristic curves C1 and C2 are for a normal solar cell module and a solar cell module in which an abnormality has occurred, as in the case of FIG. The characteristic curve C1a is for a normal solar cell module when the amount of incident light decreases, and the characteristic curve C2a is for a solar cell module in which an abnormality occurs when the amount of incident light decreases.

  In a solar cell string including a solar cell module in which an abnormality has occurred, the operating point A2 of the normal solar cell module is shifted to the operating point A3 due to a decrease in the amount of incident light, and the operation of the solar cell module in which an abnormality has occurred Point B shifts to operating point B1. Thus, a voltage shift amount ΔIa that is substantially proportional to the change in the amount of incident light occurs, and the operating point current changes greatly. On the other hand, even if the amount of incident light changes greatly, the amount of voltage change between the operating points A2 and A3 and the amount of voltage change between the operating points B and B1 are very small. Therefore, the shift amount ΔVa of the midpoint potential V (m) hardly changes from the shift amount ΔV when the incident light amount is large, and the abnormality determination can be accurately performed without being influenced by the increase or decrease of the incident light amount.

  Further, when the abnormality determination of the solar cell string is performed using the midpoint potential V (m), as described above, in the solar cell string in which the abnormality has occurred, the solar cell module in which the abnormality has occurred Which side is connected to the midpoint position can also be detected. As shown in FIG. 4A, in the solar cell string 2 (m), the value of the midpoint potential V (m) is the solar cell module 7 (m, n) determined by the power generation characteristics. If each solar cell module 7 (m, n) has the same characteristics, the midpoint potential V (m) is almost 0V.

  As shown in FIG. 4B, an abnormality has occurred in the solar cell module on the negative terminal 2b (m) side, for example, the solar cell module 7 (m, 9) with respect to the midpoint position 8 (m). In this case, the midpoint potential V (m) shifts to the negative side with respect to the reference midpoint potential. On the other hand, as shown in FIG. 4 (c), the solar cell module on the positive side terminal 2a (m) side with respect to the midpoint position 8 (m), for example, the solar cell module 7 (m, 2). If an abnormality occurs, the midpoint potential V (m) is shifted to the positive side. Therefore, when an abnormality is detected in a solar cell string in which a large number of solar cell modules are arranged, it is possible to identify a solar cell module in which an abnormality has occurred more efficiently than in the past.

  Next, the method of detecting an abnormality of the solar cell string 2 (m) using the midpoint potential V (m) has an advantage that the presence / absence of a ground fault to the GND potential that cannot be normally detected can be detected. If such a ground fault can be detected, it is possible to prevent the occurrence of a two-point ground fault that causes a fire of the solar cell string.

  More specifically, the midpoint potential V (m) varies according to the control operation of the power conditioner 5, does not necessarily match the GND potential, and always varies. In the solar cell string 2 (m), when the wiring portion between the solar cell modules 7 (m, 5) and 7 (m, 6) is grounded to the GND potential, an offset or fluctuation of the midpoint potential V (m) is caused. I can't see it. Therefore, when the state where the midpoint potential V (m) does not change with a constant value continues, it can be determined that a ground fault to the GND potential has occurred.

  Here, the conventional ground fault detection method generally monitors the leakage current that is the difference between the positive terminal current and the negative terminal current in the solar cell string 2 (m), and based on this, the occurrence of the ground fault is monitored. The presence or absence is determined. When the solar cell string 2 (m) has a ground fault to the GND potential at the midpoint position 8 (m), the leakage current is substantially zero, and thus the occurrence of a ground fault at such a GND potential level is detected. Can not. In the case where such a ground fault state at the GND potential level is left unattended, if a ground fault occurs in another wiring portion in the solar cell string 2 (m) and falls into a two-point ground fault state, the gap between the two ground faults There is a risk that a large current will flow through the solar cell module and cause excessive heat generation and fire. By monitoring the midpoint potential V (m), such a two-point ground fault can be prevented from occurring.

  As described above, in the solar power generation device 1 according to the present embodiment, the controller 6 has the midpoint potential V (m) of each solar cell string 2 (m) obtained from each detection unit 9 (m). Is monitoring. Further, the controller 6 functions as a determination unit that determines that an abnormality has occurred when the midpoint potential V (m) is largely shifted in the positive direction or the non-direction from the value in the normal state. Compared to the conventional method of detecting abnormality by monitoring the terminal current of the solar cell string, the S / N ratio of abnormality detection is very high, and it is always accurate without being affected by fluctuations in the amount of incident light. Anomaly detection can be performed. Further, it is possible to detect an abnormality at a lower cost than in the case of current detection. Furthermore, there is an advantage that the occurrence of ground fault to the GND potential can be detected together with the abnormality detection.

DESCRIPTION OF SYMBOLS 1 Solar power generation device 2 (m) Solar cell string 2a (m) Positive side terminal 2b (m) Negative side terminal 3 Solar cell array 4 Connection box 5 Power conditioner 6 Controller 7 (m, n) Solar cell module 8 ( m) Midpoint position 9 (m) Detection unit 11 Input unit 12 Display unit 13 Solar cell 14 Cluster V (m) Midpoint potential

Claims (5)

A solar cell string abnormality detection method comprising a plurality of solar cell modules connected in series between a positive terminal and a negative terminal,
Monitoring a midpoint potential which is a potential at a midpoint position between the positive terminal and the negative terminal of the solar cell string;
Based on the midpoint potential, detecting that an abnormality has occurred in any of the solar cell modules,
An abnormality detection method for a solar cell string, characterized in that: When the midpoint potential is shifted to the positive side with respect to a predetermined reference midpoint potential, the solar cell modules arranged between the positive side terminal and the midpoint position in the solar cell string It ’s determined that something has gone wrong,
When the midpoint potential is shifted to the negative side with respect to the reference midpoint potential, any of the solar cell modules arranged between the negative terminal and the midpoint position in the solar cell string. Judge that crab abnormality has occurred,
The abnormality detection method for a solar cell string according to claim 1. Based on the midpoint potential, it is detected that a ground fault has occurred with respect to a circuit ground potential at the midpoint position of the solar cell string.
The solar cell string abnormality detection method according to claim 1 or 2. An abnormality detection device for detecting an abnormality of a solar cell string using the method according to any one of claims 1 to 3,
A detection unit that detects a midpoint potential that is a potential at a midpoint position between the positive terminal and the negative terminal of the solar cell string;
A determination unit that determines whether an abnormality has occurred in any of the solar cell modules based on the midpoint potential detected by the detection unit;
An abnormality detecting device for a solar cell string, characterized by comprising: Multiple sets of solar cell strings;
A power conditioner for converting the generated power of each of the solar cell strings connected in parallel to AC power;
An abnormality detection device for detecting an abnormality of each of the solar cell strings,
The solar power generation device, wherein the abnormality detection device is the abnormality detection device according to claim 4.