JP2016093048A - Solar cell string working point detection method, solar cell string problem detection method, system and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem of a conventional method for detecting problems of a solar cell string by using a current value monitor that detection of problems is difficult because a change in the current of the solar cell string before and after generation is small, and monitor interval is too long when one solar cell panel, included in a solar cell string, does not generate power.SOLUTION: A monitoring slave unit for connection with a solar cell string detects the positional relationship of the maximum power working point of the solar cell and the actual working point, by analyzing the power/voltage information of the solar cell string on the basis of the power/voltage information of the solar cell strings collected by the current sensor at millisecond intervals, and can thereby detect the failure/problem of a solar cell panel constituting a solar cell string with higher accuracy.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a failure detection of a solar power generation system, particularly a solar cell panel of a solar cell string.

  A solar cell panel in a solar power generation system may have a reduced power generation amount due to an influence such as failure, aging, or shadow. In order to prevent a decrease in the amount of power generation, there is a technique for monitoring a power generation situation and transmitting measurement data using a DC power line to detect a malfunction of the solar cell panel.

  When monitoring the power generation status for each solar cell panel, the voltage / current is measured for each solar cell panel, so detection is easy even with a slight decrease in power generation. In a large-scale photovoltaic power generation system such as mega solar, the number of solar panels is enormous, and the number of slave units installed for each solar panel becomes enormous. Measurement in units of directly connected strings is common.

  However, since the solar cell string is formed by connecting about 10 to 20 solar cell panels in series, one of the solar cell panels does not generate power, and the voltage of the solar cell panel becomes zero. Even so, the change in the current of the string is small (P.30 of Non-Patent Document 1), and it is difficult to detect a fault by monitoring the current value.

  If the defect detection accuracy is high, it is possible to reduce power generation loss by replacing and repairing the defective solar cell panel.

Patent 5419018 JP 2013-80745 A

Kazuhiko Kato “Solar Power Generation System Failure Case Files”, Nikkan Kogyo Shimbun, 2010 ”

  It is a problem to accurately detect defects in the solar cell panel constituting the solar cell string from the measured values of the current and voltage of the solar cell string.

The present invention relates to a method for detecting an operating point of a solar cell string constituting a solar cell array described below,
A defect detection method, system, and apparatus can be provided.
(1)
A solar cell string operating point detection method for a solar cell array connected to a PCS (power conditioner),
A monitoring cordless handset connected to each solar cell string and monitoring the operating status of the solar cell string,
Each monitoring slave unit measures the voltage / power at which the solar cell string operates at a predetermined measurement cycle, calculates voltage change / power change information, and determines the predetermined value of the solar cell string based on the voltage change / power change information. Estimating the distance between the maximum power operating point and the operating point during the predetermined period for each predetermined period;
The solar cell string operating point detection method characterized by the above-mentioned.

(2)
(1) The voltage change / power change information of the solar cell string is voltage change information calculated by the following formula (1) and power change information calculated by the formula (2). Solar cell string operating point detection method. However, ΔV is a change in voltage of the solar cell string for each measurement period, ΔP is a change in power, and sign is a sign of ΔV, which is +1 or −1.
(3)
The distance between the maximum power operating point and the operating point in the predetermined period of the solar cell string is a numerical value calculated by the following equation (3), and the solar cell string operation described in (2) Point detection method. However, Σ is the total sum in a predetermined period.

(4)
(1) It is the solar cell string malfunction detection method of the solar cell array connected to PCS using the solar cell string operating point detection method in any one of (3),
Furthermore, a monitoring master unit that detects a malfunction of the solar cell string based on the monitoring information of the monitoring slave unit,
The monitoring slave unit and the monitoring master unit communicate with each other via a power line, wireless or wired connection,
The monitoring base unit detects a malfunction of the solar cell string constituting the solar cell array based on the distance between the maximum power operating point and the operating point of the solar cell string estimated by the monitoring slave unit in the predetermined period. To detect,
A solar cell string defect detection method characterized by the above.
(5)
Determining that any of the solar cell strings in the solar cell array is defective when the distance between the maximum power operating point and the operating point of the solar cell string in the predetermined period is equal to or less than a predetermined negative threshold. The solar cell string defect detection method described in (4), which is characterized.

(6)
A solar cell string fault detection system for detecting a fault of a solar cell string constituting a solar cell array of a solar cell array connected to a PCS,
A solar cell string fault detection system using the solar cell string fault detection method described in (5).

(7)
A solar cell string fault detection device for detecting a fault of a solar cell string constituting a solar cell array of a solar cell array connected to a PCS,
A solar cell string fault detection apparatus using the solar cell string fault detection method described in (5).

Without stopping the photovoltaic power generation, it is possible to accurately estimate the position of the operating point of the solar cell in string units with respect to the maximum power operating point, and it is possible to detect a malfunction of the solar cell with high accuracy.
Thereby, a power generation loss can be reduced.

It is explanatory drawing (Example 1) of a structure at the time of applying to the solar energy power generation system of this invention. It is a block block diagram of the monitoring communication subunit | mobile_unit 1 of this invention. (A) figure, (b) figure are the schematic diagrams of the voltage waveform and current waveform of a solar cell string. FIGS. 5A and 5B are schematic diagrams of graphs of current-voltage characteristics and power-voltage characteristics of solar cell strings, and are characteristic curves at the time of A) normal operation and B) at the time of malfunction. It is a schematic diagram of the graph of the differential characteristic (dP / dV) regarding the voltage of the electric power of a solar cell string, and is a characteristic curve at the time of A) normal time and B) malfunction. Voltage waveform (FIG. 6 (a)), voltage differential waveform (dV / dt) (FIG. 6 (b)), current waveform (FIG. 6 (c)) at the time of solar cell string A) normal, B) malfunction It is a waveform (FIG. 6 (df)) of a power waveform (FIG. 6 (d)), a power differential waveform (dP / dt) (FIG. 6 (e)), and (ΔP × sign (ΔV)). (A) figure, (b) figure, (c) figure is the schematic diagram of the differential characteristic (dP / dV) regarding the voltage of electric power with respect to the operating point of a solar cell string, the value of Formula 1, the value of Formula 2. It is.

  The monitoring unit of the solar cell string is provided with a function capable of detecting the operating point of the solar cell string.

  The string current and voltage are continuously measured and calculated by a one-chip microcomputer to collect information that can estimate the operating point of the solar cell string. In photovoltaic power generation monitoring, normally measured voltage values, current values, etc. are transmitted individually by communication means. In this case, the data interval obtained by communication is a few seconds or longer, and the measurement time interval is long. And fluctuations of current in a short time cannot be captured. Therefore, calculation is performed based on the voltage value and the current value at the stage of the handset before communication, and information about the operating point of the solar cell string is generated and transmitted.

  Since the voltage of the string of the solar cell tracks the maximum power operating point by the PCS of the photovoltaic power generation system, the voltage is generally modulated, and the string current also changes due to this voltage modulation. .

  As information on the voltage change, the integrated value of the absolute value of the voltage change ΔV,

Calculate the value of.
Next, as information on the power change, first, the product of the voltage value V and the current value I is calculated to obtain the power value P (V × I), and the sign of the voltage value change ΔV is added to the power value change ΔP. Accumulate the multiplied items.

  Obtaining these two pieces of information, that is, information relating to voltage change and information relating to power change, from these two pieces of information,

Calculate
The value of Equation 3 corresponds to the ratio of the power change to the voltage change of the solar cell string, that is, the differential characteristic (dP / dV) related to the voltage of the power.

  If the value of Equation 3 is 0, the operating point of the solar cell is the maximum power operating point, and if this value is negative, the operating point of the solar cell is higher than the voltage at the maximum power operating point. .

  The absolute value of the value of Equation 3 indicates how far the operating point of the solar cell is from the maximum power operating point. As a result, it is possible to detect whether or not the solar cell panel included in the solar cell string is defective.

  FIG. 7 schematically shows a graph of the differential characteristic (dP / dV) regarding the voltage of power, the value of Equation 1, and the value of Equation 2 with respect to the operating point of the solar cell string. The horizontal axis of the graph represents the ratio of the maximum power operating point voltage Vmp of the solar cell string to the voltage Va (= PCS input voltage) of the solar cell array.

  When a malfunction occurs in the solar cell string and the maximum power operating point voltage Vmp of the solar cell string decreases and deviates from the voltage Va of the solar cell array, dP / dV decreases corresponding to the degree of deviation, and Equation 2 The value of also decreases.

On the other hand, the value of Equation 1 is determined by the magnitude of the modulation voltage by the PCS, and is generally almost constant with respect to the voltage of the solar cell string.
Therefore, since the value of Expression 3 is the ratio of the value of Expression 2 to the value of Expression 1, it is the same characteristic as the value of Expression 2, which is equivalent to the differential characteristic (dP / dV) related to the voltage of power. It has the following characteristics.

  FIG. 1 is an explanatory diagram of a configuration when Embodiment 1 of the present invention is applied to a photovoltaic power generation system. In FIG. 1, a monitoring communication slave unit 1 performs solar power generation monitoring including solar power generation operating point detection according to the present invention, and transmits data to the monitoring communication master unit 2 by power line communication. The communication means described in Patent Document 1 can be used for this data transmission.

  A plurality of solar cell panels 3 (3 in this example) are connected in series, and the generated power is transmitted to a PCS (power conditioner) 5 via a backflow prevention diode 4. The solar cell string 6 is formed by connecting the plurality of solar cells 3 in series, and a solar cell array 8 in which a plurality of (3 in this example) solar cell pass strings 6 are connected in parallel is connected to the PCS 5. Connected.

  The current sensor 7 measures each current for each solar cell string 6 and includes a shunt resistor or a Hall element and a measurement amplifier.

  FIG. 2 is a block diagram of the monitoring communication slave unit 1 of the present invention. In FIG. 2, the voltage connection is connected to the input voltage of the PCS 5, which is approximately equal to the voltage of the solar cell string 6. The voltage divider 11 divides the voltage of the voltage connection terminal with a resistor and outputs a voltage proportional to the voltage between the voltage connection terminals.

  The signal switch 12 selects any one of a voltage proportional to a voltage connection voltage, a voltage corresponding to each of a plurality of current value inputs, and an output voltage of the temperature sensor 16. This voltage is converted from an analog value to a digital value by the A / D converter 13.

  The digital information of these voltage values is input to the CPU 14, and a photovoltaic power generation operating point detection calculation is performed by a calculation process described later. Moreover, CPU14 modulates data, such as a photovoltaic power generation operating point, a solar cell string voltage, and a solar cell string current, by the method of patent document 1, and produces | generates a transmission signal. The transmission signal is output to the voltage connection terminal by the driver 15 in the form of a signal suitable for power line communication.

  As the signal switcher 12, the A / D converter 13, and the CPU 14, a one-chip microcomputer or the like can be used.

  The voltage of the solar cell string 6 is usually equal to the voltage of the solar cell array 8, and the voltage is generally modulated in order to track the maximum power operating point by the PCS 5 of the photovoltaic power generation system. The string current also changes due to the modulation.

  A graph schematically showing the waveform of the voltage modulation and current modulation is shown in FIG. At the maximum power operating point, the voltage modulation waveform and the current modulation waveform are in opposite phase and have the same modulation rate.

In the photovoltaic power generation monitoring slave of the present invention, the voltage change and current change of the string generated by this voltage modulation are detected as follows.
4A and 4B are schematic diagrams of graphs of current-voltage characteristics and power-voltage characteristics of the solar cell string.

  In the graph of FIG. 4, (A) shows the characteristics of a normal solar cell string, and (B) shows the characteristics of a solar cell string having a problem that a part of the solar cell panel constituting the string does not generate power. As illustrated, in the graph of (B), the voltage Vmp at the maximum power operating point is lower than that of the normal one.

  In a solar power generation system, it is considered that most of the solar cell strings are normally operating normally. In this case, the voltage of the solar cell strings connected in parallel is centered on the voltage Vmp of the maximum power operating point of the solar cell string. It is considered that the modulation voltage from the PCS is superimposed on.

  In a normal solar cell string, since the voltage Vmp at the maximum power operating point and the voltage Va of the solar cell array are substantially equal, the voltage changes with the modulation voltage as indicated by an arrow in the figure centering on Va.

  In FIG. 4B, since (A) is the maximum power operating point, the change in the power value is small even when the voltage changes due to the modulation voltage. However, in (B), Va is the maximum power operating point Vmp. Therefore, as is clear from the graph of FIG. 4, when the voltage increases in the voltage near Va, the power decreases.

  FIG. 5 is a schematic diagram of a graph of the differential characteristic (dP / dV) with respect to the voltage (V) of the power (P) of the solar cell string, and schematically shows a characteristic curve when A) is normal and B) is defective. It is a thing.

  At any maximum power operating point at the time of A) normal operation and B) at the time of malfunction, the power is the maximum value, and the ratio of the power change with respect to the voltage is almost 0, so dP / dV is always 0. Also, dP / dV is negative at voltages higher than the maximum power operating point.

  6 (a) to 6 (f) show the voltage waveform, the voltage time differential waveform (dV / dt), the current waveform, the power waveform, and the power when the solar cell string is A) normal and B) malfunction, respectively. The waveform of the time differentiation waveform (dP / dt) and (ΔP × sign (ΔV)) is schematically shown.

  In each diagram of FIG. 6, the time interval of one period of the modulation waveform is indicated by a vertical dotted line in the diagram. This time interval is a modulation period by the PCS, and is generally in the range of several milliseconds to several seconds. For convenience of explanation, the waveform shown in the figure has a modulation amplitude larger than the actual amplitude.

  6C and 6A correspond to the current-voltage characteristics (A) and (B) shown in FIG. The point is the maximum power operating point when normal, and the voltage is higher than the maximum power operating point when there is a malfunction.

Under normal conditions, the amplitude of the voltage and the amplitude of the current are substantially the same and the phases are opposite, the pulsating flow of the power waveform is small, and the time differential waveform (dP / dt) of the power is also small.
At the time of malfunction, the current amplitude is large and the phase is opposite to the voltage amplitude. The pulsating portion of the power waveform is large as shown in the figure, and the time differential waveform (dP / dt) of the power is also large.

  From this relationship, it is possible to know the positional relationship with the maximum power operating point at the operating voltage (operating point) by examining the relationship between the change in voltage and the change in power. A suitable calculation process for this will be specifically described below.

In the photovoltaic power generation monitoring slave unit, the current and voltage of the string are measured (sampled) every 1 millisecond. This is because the period of voltage modulation in the PCS is in the range of several milliseconds to several seconds, and it is preferable to acquire the voltage value and the current value at a time interval shorter than that period.
The CPU 14 calculates the power value from the measured voltage value and current value.

  The difference between the voltage value and the power value at the current measurement point and the previous measurement point is calculated, and the difference between the voltage values is ΔV and the difference between the power values is ΔP. ΔV may be positive or negative depending on the sampling timing.

In the case of (A), ΔP is substantially 0 from the graph of the relationship between power and voltage in FIG.
In the case of (B), from the graph of the relationship between power and voltage in FIG. 4, ΔP is negative when ΔV is positive, and ΔP is positive when ΔV is negative.

  In order to eliminate the influence of the sign of ΔV, the present invention is characterized in that ΔP × sign (ΔV) is calculated. Here, sign is a function that gives −1 if the argument is negative and gives 1 if the argument is positive.

In the case of (A), ΔP × sign (ΔV) is almost zero.
In the case of (B), ΔP × sign (ΔV) is negative.

  Similarly, ΔP × sign (ΔV) is positive if the maximum power operating point is higher than Vmp.

  Furthermore, the magnitude of the absolute value of ΔP × sign (ΔV) is proportional to the difference between the voltage at the maximum power operating point and the voltage of Vmp.

  In the first embodiment, as information regarding the voltage change, an integrated value of the absolute value of the voltage change ΔV,

  Calculate the value of. In addition, as information related to the power change, first, the product of the voltage value and the current value is calculated to obtain the power value P, and the power value change multiplied by the sign of the voltage value change is integrated.

  At this time, the integration time is, for example, a communication frequency (several tens of seconds) in solar power generation monitoring.

  From the above two pieces of information, that is, the information Σ | ΔV | regarding the voltage change and the information Σ (ΔP × sign (ΔV)) relating to the power change,

を計算する。この値は、太陽電池動作点の最大電力動作点からのずれ量に相当する。

Calculate This value corresponds to the amount of deviation of the solar cell operating point from the maximum power operating point.

  If this value is 0, the operating point of the solar cell is the maximum power operating point, and if this value is negative, the voltage at the operating point of the solar cell is higher than the voltage at the maximum power operating point. The absolute value of this value indicates how far the operating point of the solar cell is from the maximum power operating point.

  As a result, it is possible to detect whether or not the solar cell panel included in the solar cell string has a defect. Therefore, the defective solar cell panel may be appropriately replaced.

  Note that the above two pieces of information are two numerical values for the integration period, and this data may be transmitted to the parent device and the calculation of Equation 7 may be executed by the parent device. In this case, since the division operation is performed not by the slave unit but by the master unit, the calculation resources of the microcomputer of the slave unit can be saved.

  An experiment using a prototype circuit for detecting a photovoltaic power generation operating point according to the present invention will be described. Experimental results simulating the amount of deviation of the solar cell operating point from the maximum power operating point when the solar cell string is composed of 10 solar cell panels and the PCS modulation is a 276 Hz sine wave are shown below. The data sampling period is 0.75 milliseconds, and the integration period is 35 seconds.

  In this simulation, the voltage at the maximum power operating point of the solar cell string is equal to the voltage at the maximum power operating point of the solar cell array when normal, and one of the 10 solar cell panels constituting the string when malfunction occurs Is in a state where the bypass diode is conductive and the voltage at the maximum power operating point of the solar cell string is equal to 9/10 of the voltage at the maximum power operating point of the solar cell array.

  As a result of the simulation, the detection value at normal time was 10, and the detection value at malfunction was -62. The detection value at normal time is ideally 0, but the value of the experimental result is considered to be close to 0 due to the influence of measurement error and noise. By setting the threshold value at the time of failure detection to, for example, 1/3 of the above detection value, it is possible to detect power generation failure of about half of the clusters of one solar cell panel.

  If this threshold is too small, erroneous detection due to the influence of noise or the like at the time of measurement occurs, and if it is too large, minor problems cannot be detected. It is preferable to optimize the threshold based on this point.

  In the photovoltaic power generation operation point detection according to the present invention, even when a part of the solar cell panel constituting the solar cell string gradually changes its characteristics due to deterioration due to secular change or the like, the deviation of the operation point is detected as a result. Therefore, it is effective for detecting a cell failure due to a gradual power reduction.

  Since the present invention detects how much the operating point of the solar cell string is from the maximum power operating point, the presence of a solar cell panel having a defect such as a voltage drop among the solar cell panels constituting the solar cell string It is possible to detect a deviation from the maximum power operating point.

  On the other hand, when the amount of power generation decreases uniformly in all of the solar cell panels that make up the solar cell string, such as when it is cloudy, the operating point of the solar cell string is close to the maximum power operating point. The possibility of misrecognizing the situation as a malfunction is considered low.

  In the present invention, as described above, since the operating point of the solar cell string detects the amount of deviation from the maximum power operating point, the characteristics of the solar cell panel constituting the solar cell string change uniformly. In the present invention, for example, such a problem that the surface of the solar cell panel constituting the photovoltaic power generation system is uniformly soiled by dust or the like and the power generation amount is reduced cannot be detected.

  However, this type of defect is effective when the conventional method for detecting a decrease in the amount of power generation is effective, and it can occur in practice by using the conventional method for detecting a decrease in generated power or generated current and the method of the present invention in combination. It is considered that all defects can be detected.

1 Monitoring Communication Unit 2 Monitoring Communication Unit 3 Solar Panel 4 Backflow Prevention Diode 5 Power Conditioner (PCS)
6 Solar cell string 7 Current sensor 8 Solar cell array 11 Voltage divider 12 Signal switcher 13 A / D converter 14 CPU
15 Driver 16 Temperature sensor

Claims (7)

A solar cell string operating point detection method for a solar cell array connected to a PCS (power conditioner),
A monitoring cordless handset connected to each solar cell string and monitoring the operating status of the solar cell string,
Each monitoring slave unit measures the voltage / power at which the solar cell string operates at a predetermined measurement cycle, calculates voltage change / power change information, and determines the predetermined value of the solar cell string based on the voltage change / power change information. Estimating the distance between the maximum power operating point and the operating point during the predetermined period for each predetermined period;
The solar cell string operating point detection method characterized by the above-mentioned. 2. The solar cell string according to claim 1, wherein the voltage change / power change information of the solar cell string is voltage change information calculated by the following equation 8 and power change information calculated by the following equation 9: Operating point detection method. However, ΔV is a change in voltage of the solar cell string for each measurement period, ΔP is a change in power, and sign is a sign of ΔV, which is +1 or −1.

The solar cell string operating point detection method according to claim 2, wherein the distance between the maximum power operating point and the operating point in the predetermined period of the solar cell string is a numerical value calculated by the following equation. However, Σ is the total sum in a predetermined period.

A solar cell string fault detection method for a solar cell array connected to a PCS using the solar cell string operating point detection method according to any one of claims 1 to 3,
Furthermore, a monitoring master unit that detects a malfunction of the solar cell string based on the monitoring information of the monitoring slave unit,
The monitoring slave unit and the monitoring master unit communicate with each other via a power line, wireless or wired connection,
The monitoring base unit detects a malfunction of the solar cell string constituting the solar cell array based on the distance between the maximum power operating point and the operating point of the solar cell string estimated by the monitoring slave unit in the predetermined period. To detect,
A solar cell string defect detection method characterized by the above.   Determining that any of the solar cell strings in the solar cell array is defective when the distance between the maximum power operating point and the operating point of the solar cell string in the predetermined period is equal to or less than a predetermined negative threshold. The solar cell string fault detection method according to claim 4, wherein the solar cell string fault detection method is characterized. A solar cell string fault detection system for detecting a fault of a solar cell string constituting a solar cell array of a solar cell array connected to a PCS,
A solar cell string fault detection system using the solar cell string fault detection method according to claim 5. A solar cell string fault detection device for detecting a fault of a solar cell string constituting a solar cell array of a solar cell array connected to a PCS,
A solar cell string fault detection apparatus using the solar cell string fault detection method according to claim 5.

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