JP2019221083A - Method and apparatus for diagnosing solar cell module - Google Patents

Abstract

To detect the deterioration of a shunt resistance Rof a solar cell module without using past data, and identify the cause.SOLUTION: A solar cell module is diagnosed by obtaining a frequency spectrum of the impedance and phase angle of the solar cell module by continuously changing the frequency of an input AC signal while the solar cell module is put in a light-shielded state (S01), by calculating the frequency spectrum of the capacitance constituting an equivalent circuit of the solar cell module in the light-shielded state from the obtained frequency spectrum of the impedance and phase angle of the solar cell module (S02), and by comparing the capacitance value on the lower frequency side than the cutoff frequency and the capacitance value on the higher frequency side than the cutoff frequency in the frequency spectrum of the capacitance of the solar cell module (S08).SELECTED DRAWING: Figure 15

Description

  The present invention relates to a method and an apparatus for diagnosing a solar cell module used for photovoltaic power generation.

  Photovoltaic power generation is composed of many components such as solar cell modules, mounts, wiring, power conditioners, and transformers. Since a photovoltaic power generation site is usually assumed to use equipment for a long period of 20 years or more, it is necessary to secure stable equipment operation throughout the usage period. For this reason, proper maintenance of the equipment is important, and among them, the solar cell module is placed in a harsh environment exposed to direct sunlight, wind and rain, and ensuring long-term reliability is the most important component. Therefore, technology for correctly grasping the state of deterioration of the solar cell module is required for equipment maintenance at the power generation site.

The silicon-based solar cell module has a structure in which silicon cells having a PN junction are arranged in a plane and they are connected in series by wiring called a bus bar. The cells connected by wiring are embedded in resin, sandwiched between tempered glass and a back sheet, and the ends are protected by an aluminum frame. FIG. 1 shows an equivalent circuit of the solar cell module. Numeral 11 denotes a current source which causes the cell to absorb light to generate a current, 12 denotes a diode corresponding to a PN junction of the cell, 13 denotes a shunt resistor _Rsh corresponding to a path of a leak current between terminals, and 14 denotes a wiring in the module. is a series resistance _{R s.}

Deterioration and failure of a solar cell module range from glass breakage to failure of a wiring extraction part for extracting electricity from a cell series circuit called a junction box to the outside. An abnormality involving a large change in appearance or electric output can be easily detected, but an abnormality that progresses slowly is difficult to detect. Many of these abnormalities have a cause inside the solar cell module and are reflected in the equivalent circuit of the solar cell module. For example, the deterioration of the resin that seals the cell appears as a decrease in the current from the current source 11 because the transmittance of light decreases due to the coloring of the resin accompanying the deterioration. The wiring deterioration such as peeling of solder caused by the expansion and contraction of the member appears as an increase in the series resistance R _s. The shunt resistor _Rsh is an element corresponding to a leakage current path between terminals of the solar cell module, and its value is affected by a plurality of factors such as the inside of the PN junction and resin.

Although the series resistance R _s increases with the deterioration of the solar cell module, the amount of increase in the series resistance R _{s and} the amount of decrease in the output of the solar cell module are substantially in a linear relationship, and from the initial stage of deterioration to the output of the solar cell module. A large impact. On the other hand, the shunt resistance R _sh decreases due to the deterioration of the solar cell module. However, if the deterioration of the shunt resistance R _sh does not proceed significantly, the effect on the output of the solar cell module cannot be seen. There is a characteristic that it decreases rapidly when it starts to decrease. The most prominent in degradation of the shunt resistor R _sh is known as PID (Potential Induced Degradation) phenomenon. The PID is a phenomenon in which the ions derived from glass move under the influence of an electric field (potential) and accumulate at the cell interface, thereby deteriorating the diode characteristics of the PN junction. Since the PID rapidly deteriorated in a short period of time and the output sharply decreased, the detection was relatively easy. However, what causes the deterioration of the shunt resistance R _sh is not limited to the PID phenomenon, and the shunt resistance R _sh is a parameter that needs to be continuously monitored in the maintenance of the photovoltaic power generation.

Typical inspection methods used for maintenance of the solar cell module include visual inspection, IV (current-voltage) characteristic inspection, and infrared image inspection. Among them, there is an advantage that the IV characteristic inspection is relatively easy and the deterioration can be quantified. If IV characteristic inspection difficult by visual inspection, infrared imaging tests, it is also possible to isolate a series resistance R _s and the shunt resistance R _sh respective degradation. Since the deterioration of the series resistance R _s and the decrease of the module output are approximately proportional to each other, if the cause of the deterioration can be specified to be the series resistance R _s , the progress of the subsequent output decrease can be roughly estimated, and the necessity of measures is necessary. And see when. If the cause of the deterioration is the shunt resistance _Rsh , the output may be abruptly reduced if it is caused by the PID phenomenon.

However, in the case of the deterioration of the shunt resistance _Rsh, a plurality of factors such as a resin for sealing the cell can be considered as a cause of the deterioration in addition to the PN junction of the cell causing the PID phenomenon. For this reason, it is desirable to further isolate the cause of deterioration of the shunt resistance _Rsh from the viewpoint of solar cell module maintenance. If the PN junction of the cell is deteriorated, its progress is relatively quick, and it is necessary to swiftly respond. On the other hand, if the resin is deteriorated, the progress is relatively slow because the change with time due to light irradiation is a cause. This is because they can be expected, and the measures to be taken are different. However, in the IV characteristic test, whether the cause is a PN junction or a resin, it is expressed by the same element (shunt resistor 13) on an equivalent circuit, and it is difficult to identify the cause.

Known methods for isolating the cause of deterioration of the shunt resistor _Rsh include an EL (Electroluminescence) inspection, an insulation resistance measurement, and an impedance measurement method. The EL inspection is a method in which light emitted by a band-to-band transition in a silicon cell caused by flowing a current between terminals of a solar cell module is captured by a camera. When the PN junction of the cell is deteriorated, the light emission luminance is reduced due to an increase in non-light-emitting transition, so that the deterioration of the cell can be visualized. However, a leakage current that does not pass through the cell also causes a decrease in light emission luminance, so that it is difficult to grasp quantitative deterioration. In addition, since a relatively large power supply is required to allow a current to flow between the terminals, the power supply is often used indoors for inspection, and it is difficult to perform inspection at an actual power generation site.

Insulation resistance measurement is a method of inspecting the insulation of a resin by measuring the insulation resistance between one terminal or both short-circuited terminals and a frame of a solar cell module. When the resin is deteriorated and the insulation property is reduced, the leakage current between the terminals is increased, so that a change in the shunt resistance _Rsh caused by a current path other than the cell can be grasped. However, the measurement of insulation resistance is greatly affected by the temperature and humidity, the state of dirt on the module surface, and the like, so that it is difficult to grasp quantitative deterioration.

  Impedance measurement is a method of applying a minute AC signal between terminals of a solar cell module and examining the frequency characteristics of impedance. Patent Document 1 discloses a method of diagnosing a solar cell module using impedance frequency characteristics between both terminals of the solar cell module and between a terminal and a frame. According to this, first, a frequency spectrum of impedance between terminals or between a terminal and a frame is obtained. From the obtained frequency characteristics, the values (equivalent circuit constants) of the elements constituting the equivalent circuit to be measured are determined by fitting. In the fitting, an equivalent circuit constant is selected so as to best reproduce the entire frequency spectrum. Therefore, the constant of each element of the equivalent circuit has one value in all measured frequency regions. Next, those values are normalized by the equivalent circuit constants obtained in a state where they have not deteriorated. Deterioration determination is performed by comparing the standardized value with a preset threshold value.

WO 2015/163329

S. M. Sze & KWOK K. NG, “Physics of semiconductor devices (Third Edition)” John Wiley & Sons, Inc., Publication, U.S.A., April 10, 2006, p.119

Deterioration of the solar cell module, depending on its cause, has the potential danger of causing a sharp drop in output. Therefore, there is a need for an inspection technique capable of detecting deterioration and isolating the cause. The IV characteristic inspection can detect the deterioration, but cannot determine the cause when the shunt resistance _Rsh has deteriorated. Although it is possible to isolate the cause degradation of the shunt resistor R _sh According to the impedance measurement is disclosed in Patent Document 1, it has been standardized by the circuit constant in a state where not deteriorated in the process. For this reason, information on the circuit constants in a state where the deterioration has not occurred is required. If this value is unknown, the diagnosis of deterioration cannot be performed. In the case where the maintenance management business of the photovoltaic power generation site is undertaken halfway, it can easily occur that information in the initial state of the solar cell module does not exist.

Therefore, it is necessary to develop a method of detecting deterioration of the shunt resistance _Rsh of the solar cell module and identifying the cause without using past data such as data in a state where the module is not deteriorated.

  A method for diagnosing a solar cell module according to an embodiment of the present invention is a method for continuously changing the frequency of an input AC signal while setting the solar cell module in a light-shielded state to obtain a frequency spectrum of impedance and phase angle of the solar cell module. From the obtained frequency spectrum of the impedance and phase angle of the solar cell module, the frequency spectrum of the capacitance constituting the equivalent circuit of the solar cell module in the light-shielded state is calculated, and the frequency spectrum of the capacitance of the solar cell module is obtained. In the above, the solar cell module is diagnosed by comparing the capacitance value on the lower frequency side than the cutoff frequency with the capacitance value on the higher frequency side than the cutoff frequency.

  Deterioration of the cells constituting the solar cell module can be detected without using past data such as data in an undegraded state.

  Other problems and novel features will be apparent from the description of this specification and the accompanying drawings.

It is an equivalent circuit diagram of a solar cell module. It is a structural example of a solar power generation system. It is an equivalent circuit diagram of a solar cell module in a non-power generation state. It is an example of a measurement circuit which performs impedance measurement of a solar cell module. It is an example of measurement of the frequency spectrum of impedance Z. It is a measurement example of the frequency spectrum of the phase angle θ. It is a relational expression of impedance, phase angle, and circuit constant of a solar cell equivalent circuit in a non-power generation state. FIG. 4 is an equivalent circuit diagram of a simplified solar cell module with a limited frequency range. It is a frequency spectrum of the parallel resistance calculated from the measured value. It is a frequency spectrum of the capacitance calculated from the measured value. It is an example of measurement of the frequency spectrum of impedance Z. It is a measurement example of the frequency spectrum of the phase angle θ. It is a frequency spectrum of the parallel resistance calculated from the measured value. It is a frequency spectrum of the capacitance calculated from the measured value. It is a figure which shows the temperature dependence of the parallel resistance in a normal module and a deteriorated module. It is a figure which shows the bias voltage Vdc dependence of C_high and C_low in a normal module and a deterioration module. It is a diagram showing temperature dependence of the frequency spectrum of the capacitance C _p. It is a hardware configuration example of a solar cell module diagnosis system. It is a flowchart which determines the presence or absence of deterioration of a solar cell module. It is a flowchart which determines the presence or absence of deterioration of a solar cell module. Is a graph showing the temperature dependence of the forward resistance R _F of the theoretically obtained PN junction. It is a flowchart which determines the presence or absence of deterioration of a solar cell module.

  In this embodiment, the deterioration of the cells of the solar cell module is detected by impedance measurement.

  FIG. 2 shows a configuration example of a relatively large-scale solar power generation system. A unit in which the solar cell modules indicated by 21 are connected in series is called a string 22, and a plurality of strings 22 are connected in parallel in a connection box 24. A circuit in which the strings 22 are connected in parallel is called an array 23. The plurality of arrays 23 are further connected in a current collection box, and are input to a power conditioner (PCS) 25 therefrom. The PCS 25 converts DC power output from the solar cell into AC and sends it to the grid 27. The PCS 25 may be connected to the system 27 via the insulating transformer 26 in some cases.

  The equivalent circuit 10 of the solar cell module is as shown in FIG. 1, and a current is generated when sunlight enters the cells in the solar cell module. On the equivalent circuit, a current corresponding to the solar radiation intensity is generated. It is represented by current being supplied from the ideal constant current source 11 to be supplied. A part of the supplied current is supplied to the load from the P terminal 15 via the diode 12 and the remainder via the series resistor 14. The current supplied from the load returns to the current source 11 through the N terminal 16. The leakage current generated in the solar cell module flows through the path of the shunt resistor 13. The impedance characteristics of the solar cell module can be measured in principle even in a power generation state, but measurement in a non-power generation state is easier from the viewpoint of a measurement circuit and improvement of measurement accuracy.

Therefore, when measuring the impedance of the solar cell module at the power generation site, the measurement is performed in a state where the surface of the solar cell module (the glass surface on which sunlight enters) is shielded from light. FIG. 3 shows an equivalent circuit 30 of the solar cell module when an AC signal is applied between the P and N terminals in a light-shielded state, that is, in a state where the solar cell module does not generate power. Since no power is generated, the current source 11 is eliminated, and the diode 12 corresponding to the PN junction is represented by the capacitance C _p31 and the parallel resistance R _p32 . The shunt resistor _Rsh in the equivalent circuit in the power generation state represents the resistance to the current through the PN junction and all the resistance components corresponding to the path of the leakage current through the resin in the cell or around the cell. The parallel resistance R _p32 in the equivalent circuit of the above is a resistance representing the resistance component to the current of the PN junction path and the resistance component of the leakage current path caused by the cell. However, although the resistance of the PN junction path and the resistance of the other leakage current paths are connected in parallel, the resistance of the leakage current path other than the PN junction path is extremely smaller than the resistance of the PN junction path. R _p approximately corresponds to the resistance of the PN junction path. For this reason, the portion 33 combining the capacitance C _p 31 and the parallel resistance R _p 32 corresponds to a PN junction. In the element resulting from the wiring, an inductance L _s 34 that is found due to an AC component is newly added to the series resistance R _s 14.

  When measuring the impedance characteristics of the solar cell module, necessary safety measures such as stopping the PCS and disconnecting the string circuit including the module to be measured are implemented. Thereafter, the module is covered with a cardboard so as to cover the entire light receiving surface of the module to be measured. As a result, the solar cell is placed in a light-shielded state, thereby stopping power generation. The method used to create the light-shielded state is not limited to this. Instead of corrugated cardboard, it may be covered with a light-shielding sheet or rubber made by folding a light-shielding curtain or blue sheet multiple times, or may be measured at night.

  After being left in that state for a while to wait for the cell temperature to stabilize, the frequency spectrum of the impedance of the solar cell module is obtained. For the measurement, a measuring device such as an LCR meter or an impedance analyzer can be used. In particular, a device capable of continuously changing the frequency of an input signal (AC signal) input to the solar cell module is used. FIG. 4 shows an example of a measurement circuit for measuring the impedance of the solar cell module. The main components of the measurement circuit include a sine wave oscillator 41, a current-voltage converter 42, and a vector voltage ratio measurement unit 43, and an AC signal generated from the sine wave oscillator 41 And an output signal output from the other terminal (N terminal 16) is input to the current-voltage converter 42. The sine wave oscillator 41 includes a bias power supply 51, an oscillator 52, and a synthesis circuit 53 that synthesizes a DC bias Vdc from the bias power supply 51 and an oscillation signal from the oscillator 52 to output an AC signal. The current-voltage converter 42 converts the output signal (current signal) output from the solar cell module 40 into a voltage, a reference resistor 54, and a potential at a connection point L between the solar cell module 40 and the reference resistor 54 as a reference potential. And a control amplifier 55 for controlling the operation. The vector voltage ratio measuring unit 43 includes a first voltmeter 56 that measures an AC voltage between the P and N terminals of the solar cell module 40, and a second voltmeter 57 that measures the AC voltage across the reference resistor 54. , And a ratio meter 58 for calculating a ratio between the first voltmeter 56 and the second voltmeter 57.

  The impedance Z and the phase angle θ of the solar cell module 40 are measured by the measurement circuit shown in FIG. The impedance Z is calculated as a ratio of the magnitude of the AC voltage of the solar cell module 40 measured by the first voltmeter 56 to the magnitude of the AC current of the solar cell module 40 obtained from the control amount of the control amplifier 55. The phase angle θ is calculated from the phase difference between the AC voltage of the solar cell module 40 obtained by the first voltmeter 56 and the AC current of the solar cell module 40 obtained by the second voltmeter 57 by the ratio meter 58. Is calculated.

  Using the measurement circuit shown in FIG. 4, the measured voltage level of a polycrystalline silicon solar cell module composed of 60 cells commercially available was set to 0.1 V (effective value of an input signal (AC signal)). , The DC bias Vdc is changed to 0 V, and the frequency of the input signal is changed from 1 Hz to 100 kHz to obtain a frequency spectrum of the impedance Z and the phase angle θ. Further, the setting of the DC bias Vdc is changed to 0.1, 0.5, 1.0, 1.5, 2.0, and 2.5 V, and the frequency spectrum is acquired with each setting. This is because the solar cell module is provided with a bypass diode, and when a reverse bias is applied to the PN terminal, the bypass diode is turned on in a relatively small voltage range, and desired characteristics cannot be obtained. Therefore, by superimposing the DC bias Vdc on the input AC signal and keeping the amplitude of the AC signal sufficiently small, the applied voltage is kept at a positive value to prevent the bias diode from being turned on. The slope of the -IV characteristic is also measured in a region where the diode characteristic of the solar cell module can be regarded as substantially constant. FIG. 5A shows the measured frequency spectrum of the impedance Z of the solar cell module, and FIG. 5B shows the frequency spectrum of the phase angle θ.

From these results, the equivalent circuit constant is obtained. In the prior art, the obtained spectrum is fitted using an expression of the impedance obtained from the equivalent circuit. FIG. 6 shows a relational expression between an impedance, a phase angle, and a circuit constant of an equivalent circuit of a solar cell module in a non-power generation state. More specifically, the impedance Z is represented by a complex number, and the absolute value | Z | of Z and the phase angle θ are calculated using the real part (Re (Z)) and the imaginary part (Im (Z)) of Z, respectively ( It is expressed by equation 1). Further, Re (Z) and Im (Z) are expressed by (Equation 2) using the circuit constants of the equivalent circuit 30 shown in FIG. While the equivalent circuit 30 includes four variables of capacitance C _p , parallel resistance R _p , series resistance R _s , and inductance L _s , the equation for solving it is the impedance Z shown in (Equation 1). And the expression of the phase angle θ cannot be solved analytically, and the circuit constant has to be obtained by fitting. The notation of the absolute value | Z | of the impedance Z is used here in relation to the complex expression of the impedance, and is the value of the impedance Z measured by the measurement circuit.

In this embodiment, no fitting is used to determine the circuit constant. Series resistance R _s in the original solar cell module is the most about several Ω several milliohms, is sized to be negligible compared to the number 10kΩ from several kΩ shunt resistor R _sh or parallel resistor R _p. In addition, the size of the order of several μH also with respect to the inductance L _s. If the size of this extent, the its effect on the frequency spectrum of the impedance Z come out, in sufficiently small high frequency range the impedance of the capacitance C _p in comparison with the shunt resistor R _sh or parallel resistor R _p It is. In the case of a solar cell module, the region is a frequency region of about 100 kHz or more. This means that when the frequency spectrum is fitted by a conventional method, the values of the series resistance R _s and the inductance L _s affect the higher frequency side than about 100 kHz, and the series resistance R _s and the inductance L _s described later. _It can be confirmed by calculating the real part and the imaginary part of the impedance Z with respect to the equivalent circuit ignoring _s , and comparing the real part and the imaginary part obtained by fitting according to a conventional method.

For this reason, in the frequency spectrum measurement shown in FIGS. 5A and 5B, the frequency of the input signal is limited to 100 kHz. There is no problem to ignore the series resistance R _s and the inductance L _s if this frequency range. FIG. 7 shows a simplified equivalent circuit diagram ignoring these. The real part and the imaginary part of the impedance Z with respect to the equivalent circuit 70 are represented by (Equation 3) shown in FIG. By substituting this expression into (Expression 1), the absolute value | Z | of the impedance Z and the phase angle θ can be obtained. The feature of (Equation 3) is that, while (Equation 2) is represented by four variables, it is represented by two variables (parallel resistance R _p and capacitance C _p ). Since two equations for the absolute value | Z | of the impedance Z and the phase angle θ shown as (Equation 1) are given to the two variables, the variables can be obtained analytically. Specifically, (Equation 4) is obtained by substituting (Equation 3) into (Equation 1) to obtain variables R _p and C _p . Here, ω = 2πf (f is the frequency of the input signal). By substituting the impedance Z and the phase angle θ obtained by the measurement into (Equation 4), the equivalent circuit constants (R _p , C _p ) can be obtained. As can be seen from the expression, R _p and C _p have frequency dependence.

Although the series resistance R _s and the inductance L _s ignored from the equivalent circuit cannot be obtained, it is a great advantage that the equivalent circuit constant can be obtained without using the fitting. In the case of fitting, the reproducibility of the experimental value by the fitting function is insufficient, or the degree of coincidence between the function value in one frequency domain and the experimental value decreases in the other frequency domain. Occurs. To reduce the arbitrariness of the fitting, there are certain guidelines such as minimizing the residual sum of squares of the values obtained from the experimental data and the fitting function, but despite the uniformity of the procedure, a satisfactory fitting is achieved as a result. I do not guarantee that it will be given.

  Another advantage of the measurement method of the present embodiment is that the frequency range for measuring the frequency spectrum is limited to a relatively low frequency range, thereby simplifying the measurement system. For example, in order to measure a frequency range up to the order of MHz, an expensive device is required. Generally, the device is large, and it is necessary to pay attention to electrical connection. In particular, when measurement is performed at an outdoor power generation site, the influence of noise increases, which is disadvantageous in terms of accuracy. On the other hand, in a frequency range of about 100 kHz or less, measurement can be performed with a relatively simple device, and the influence of connection and noise on the measurement result is small.

8A and 8B show equivalent circuit constants (R _p , C _p ) calculated based on (Equation 4) from the frequency spectrum measurements shown in FIGS. 5A and 5B. Figure 8A is a frequency spectrum of the parallel resistor _{R p,} FIG. 8B is a frequency spectrum of the capacitance _{C p.}

Here, from the expressions (Expression 4) of FIG. 6, the phase angle θ is near 0 °, the parallel resistance R _{p ~} | is the absolute value of the impedance Z | | Z Z | parallel resistance most R _p It can be seen that the effect of the parallel resistance R _p is incorporated into the capacitance C _p through the denominator | Z |. On the other hand, when the phase angle θ is near −90 °, the relationship of the absolute value | Z |｜ 1 / (ωC _p ) of the impedance Z is established. Therefore, theta is the absolute value of the impedance Z at -90 ° vicinity | Z | is responsible capacitance C _p, the parallel resistor R _p in the molecule | Z | Electrostatic capacitance C _p through the repeated You can see that it gets stuck.

From the measurement result of the phase angle θ shown in FIG. 5B, the R _p value in the frequency region where the phase angle θ is near 0 ° as "R _p _Low" in FIG. 8A, the phase angle θ is -90 ° vicinity the _{C p} value of the frequency domain in FIG. 8B represented as _{"C p} _High". Here, the R _p _low and C _p _high, the absolute value of the impedance Z of the equivalent circuit | Z | relative contribution of elements each occupy the majority. When the phase angle θ is near 0 °, the absolute value | Z | of the impedance Z is determined solely by R _p _low, and C _p has almost no contribution. When the phase angle θ is near -90 °, the absolute value | Z | of the impedance Z is determined exclusively by C _p _high, and R _p has almost no contribution. That is, it is considered that R _p _low and C _p _high are circuit constants R _p , C _p that do not depend on the frequency that has been conventionally calculated by fitting. This can be confirmed from the fact that the junction capacitance of the series-connected cells constituting the module is determined by Mott-Schottky plot for C _p _high.

Next, the same method is applied to the module whose cell has deteriorated. As a module whose cell was deteriorated, a module whose output was deteriorated by about 15% due to potential induced deterioration (PID) was used as a test module. The measurement results are shown in FIGS. 9A and 9B. 9A is a frequency spectrum of impedance Z of the deteriorated solar cell module, and FIG. 9B is a frequency spectrum of phase angle θ of the deteriorated solar cell module. FIGS. 10A and 10B show equivalent circuit constants (R _p , C _p ) calculated based on (Equation 4) from the frequency spectrum measurements shown in FIGS. 9A and 9B. Figure 10A is a frequency spectrum of the parallel resistor _{R p,} FIG. 10B is a frequency spectrum of the capacitance _{C p.} When comparing FIG. 8A and FIG. 10A, it can be seen that the value of R _p _low is greatly reduced, whereas when comparing FIG. 8B and FIG. 10B, the value of C _p _high hardly changes. From this, it is expected that deterioration of the solar cell module can be detected by R _p _low. However, as shown in FIG. 11, the parallel resistor R _p is the temperature dependency is very large, the difference between the parallel resistance R _p of between module temperature is high and the normal module and the degraded module will almost gone. It is not unusual for the cell temperature to rise to about 70 ° C. in an outdoor environment where direct sunlight is radiated, and it is difficult to detect deterioration by simply comparing R _p _low. In addition, the difference in R _p _low becomes smaller as the degree of deterioration of the solar cell module decreases, and the difference from the normal module becomes smaller, so that deterioration detection becomes more difficult. On the other hand, since C _p _high has a small difference between the degradation modules normal module, prompted a high measurement accuracy for use in deterioration detection is difficult.

Therefore, in the present embodiment focuses on the capacitance of the low frequency side (denoted as "C _p _low"). C _p _low is a capacitance value seen on the lower frequency side of the frequency spectrum of the capacitance C _p shown in FIG. 8B or FIG. 10B. C _p _low has a larger value than C _p _high and shows a substantially constant value in a certain frequency range. Further, C _p _high can be classified according to a cutoff frequency fc described below.

The cutoff frequency fc is defined as follows. In the equivalent circuit shown in FIG. 7, when the input AC signal to the terminal, when the signal frequency is low, the impedance of the capacitance _{C p (1 / (ωC p} )) is large, the signal is parallel resistor preferentially R _p Pass through. On the other hand, if the signal frequency is high because the impedance of the capacitance C _p conversely decreases, the signal is preferentially passes through the capacitance C _p. In the intermediate frequency region, there is a frequency at which the impedance 1 / (ωC _p ) of the capacitance C _{p and} the impedance R _p of the parallel capacitance R _p are equal, and this frequency is defined as a cutoff frequency fc. 6 (Formula 1) and (Equation 3) easily from _{^{θ = tan -1 (-ωC p R}} p) is Michibike, phase angle and substituting the condition of a cutoff frequency _{fc R p = 1 / (ωC} p) It can be seen that the frequency at which θ becomes −45 ° corresponds to the cutoff frequency fc.

The value of the capacitance C _p of capacitance in the low frequency side of the cut-off frequency fc becomes substantially constant C_LOW, defined as C_high generally the value of the capacitance becomes constant at a high frequency side than the cut-off frequency fc I do. For example, in the frequency spectrum of the phase angle θ shown in FIG. 5B, the frequency at which the phase angle becomes −45 ° is about several tens Hz. In contrast, corresponds to a region just capacitance C _p is a number 10Hz around the frequency spectrum of the capacitance C _p shown in FIG. 8B is changed, in the high frequency side approximately 150nF, generally at 200nF at low frequency side It shows a constant value. Therefore, C_low of this solar cell module is approximately 200 nF, and C_high is approximately 150 nF. FIG. 12 shows the results of measuring C_low and C_high obtained by dividing by the cutoff frequency fc for the normal module and the deteriorated module while changing the bias voltage Vdc. It can be seen that the change in C_low is greater than the change in C_high before and after degradation. C_high is approximately equal to C _p _high, C _p _high as described earlier can be regarded as the junction capacitance C _p of the cell. Junction capacitance C _p of the cell is basically definite doping profile of the PN junction of the solar cell module. For this reason, the doping profile of the PN junction needs to change in order for this value to change significantly. However, such a change requires extremely high energy, and requires energy such as that generated by use as a solar cell. No such change occurs. On the other hand, since the phase angle θ ≒ 0 on the low frequency side, C _p １ ／ 1 / | Z | and | Z | 〜R _p from (Equation 4) in FIG. a _p, in C _p increases relationship by R _p is reduced by degradation. That is, C _p _low increases, reflecting that R _p _low is significantly reduced due to deterioration of the solar module.

Temperature dependence of the parallel resistor R _p as shown in FIG. 11 is very large, since the magnitude of the R _p at a temperature change in the number 10 degrees changes the digit, the temperature of the cell is reached during use of the power generation site parallel resistance magnitude of R _p of the normal module deterioration modules in range had almost become the same level. On the other hand, the capacitance _{C p} is hardly changed at the same temperature range as shown in FIG. 13 (T = 0~80 ℃). From (Equation 4) in FIG. 6, R _p １ ／ 1 / ωC _p , and the fact that the capacitance C _p does not change much despite the fact that the parallel resistance R _p fluctuates greatly with temperature changes is as follows. with temperature change ω (= 2πf), therefore in order to cut-off frequency fc is changed to cancel the change of the parallel resistance R _p.

As shown in FIG. 12, C_high shows almost the same value in the normal module and the deteriorated module. Further, for normal modules, C_high and C_low are approximately the same size. This is the normal module, reflecting the fact that generally the original junction capacitance value is obtained in the frequency range of interest also seeking C _p by the equation (Equation 4) in FIG.

  As described above, C_high shows almost the same value between the normal module and the deteriorated module, whereas C_low is almost the same as C_high in the normal module, but changes greatly when deteriorated. Further, both C_high and C_low have small temperature dependence. Therefore, in the first embodiment, the degree of deterioration of the solar cell module is determined by comparing the value of C_high with the value of C_low. This makes it possible to determine the degree of deterioration of the solar cell module to be evaluated, even if it does not have a normal measurement value.

  FIG. 14 shows a hardware configuration example of a solar cell module diagnosis system for diagnosing deterioration of a solar cell module according to the present embodiment. The solar cell evaluation device 100 includes a processor 101, a main memory 102, an auxiliary memory 103, an input / output interface 104, a display interface 105, an I / O port 106, and a network interface 107, which are connected by a bus 108. The input / output interface 104 is connected to an input device 109 such as a keyboard and a mouse, and the display interface 105 is connected to a display 110 to implement a GUI. The network interface 107 is an interface for connecting to a network. The auxiliary storage 103 is generally configured by a nonvolatile memory such as an HDD, a ROM, or a flash memory, and stores a program executed by the solar cell evaluation device 100, data to be processed by the program, and the like. The main memory 102 is configured by a RAM, and temporarily stores a program, data necessary for executing the program, and the like according to an instruction of the processor 101. The processor 101 executes a program loaded from the auxiliary storage 103 to the main storage 102. The solar cell evaluation device 100 can be realized by, for example, a PC (Personal Computer) or a server.

  The auxiliary memory 103 stores measurement data 120, other data, a solar cell module diagnostic program 122, and other programs. The solar cell module diagnostic program 122 includes an impedance measuring unit 122a and a deterioration evaluating unit 122b as its main parts.

  The measuring device 130 is connected to the solar cell evaluation device 100 via the I / O port 106. The measuring device 130 includes the measuring circuit shown in FIG. 4, and the measuring device 130 is connected to a solar cell module 131 to be diagnosed. The measuring device 130 acquires the frequency spectrum of the impedance Z and the phase angle θ of the solar cell module 131.

FIG. 15 shows a flowchart executed by the solar cell module diagnosis program 122 to determine whether or not the solar cell module has deteriorated. The impedance measurement unit 122a sets necessary measurement parameters such as a frequency measurement range and a bias voltage Vdc, obtains a frequency spectrum of the impedance Z and the phase angle θ of the solar cell module 131 by the measurement device 130, and stores the frequency spectrum as measurement data 120. (S01). The impedance Z, from the frequency spectrum of the phase angle theta, converts the parallel resistor _{R p,} the frequency spectrum of the capacitance _{C p,} are also stored as the measurement data 120 (S02). The deterioration evaluation unit 122b diagnoses the solar cell module using the measurement data 120. Incidentally, the degradation evaluating portion 122b, when performing diagnosis based on the capacitance C _p is converted into the frequency spectrum of the parallel resistor R _p may be omitted.

9A and 9B are shown as measurement examples of the deterioration module, but when the deterioration further progresses, in the frequency spectrum of the phase angle θ in the frequency range of 100 kHz or less, the phase angle θ does not reach −90 ° and greatly separates. The value may increase toward a positive value, or the cutoff frequency fc may not exist in the frequency range. In such a case, since the capacitance C _p of the PN junction means that has deteriorated considerably, without performing the diagnosis of the present embodiment, when the solar cell module is degraded Can be determined.

Accordingly, the minimum value of the phase angle θ, θ _min, is detected (S03), and it is evaluated whether θ _min is a value within a predetermined vicinity of −90 ° (S04). Further, the cutoff frequency fc is detected (S05). If θ _min has not reached −90 ° or more than the predetermined threshold (N in S04) or the cutoff frequency fc is not in the measurement range (N in S06), it is diagnosed that the solar cell module 131 has deteriorated. (S10). On the other hand, in cases other than these, the determination described in the present embodiment is performed. First, C_high and C_low are detected using the cutoff frequency fc (S07), and the detected C_high and C_low are compared (S08). The comparison between C_high and C_low may take the difference (| C_high−C_low |) or may calculate and use the ratio (C_low / C_high). A threshold is determined in advance according to the measurement error and the degree of deterioration to be detected. If the difference (ratio) between C_high and C_low is smaller than the threshold, it is diagnosed that there is no deterioration (S09), and the difference between C_high and C_low is determined. If the difference (ratio) is equal to or greater than the threshold, it is diagnosed that there is deterioration (S10). The obtained diagnosis result is displayed on the display 110, for example (S11). As described above, the deterioration of the solar cell module can be diagnosed even if there is no measured value in a normal state.

FIG. 16 shows another flowchart for determining whether the solar cell module has deteriorated. In the flowchart of FIG. 16, the determination of the deterioration of the solar cell module is performed only by C_low. The solar cell is required to increase the power generation efficiency to the limit in low manufacturing process, considered can not significantly alter the PN junction profile, the difference in the junction capacitance C _p if silicon-based solar cell is not so large . In other words, regardless of the cell manufacturer, the value of C_high can be expected to be substantially similar. In the flow of FIG. 16, C_high is assumed to be a predetermined value for the silicon-based solar cell, and deterioration determination is performed based on whether C_low is within a predetermined range based on the assumed C_high. In the flowchart of FIG. 16, steps for performing processing common to the flowchart of FIG. 15 are denoted by the same reference numerals, and redundant description will be omitted. In the present modified example, C_low is detected from the measurement data (S17), and whether or not there is deterioration is determined based on whether or not C_low is smaller than a predetermined threshold (S18). According to this method, there is an advantage that the frequency range acquired in step S01 can be further narrowed.

As Example 2, a description will be given of a method of performing the deterioration determination of the solar cell module with a parallel resistor R _p. This method is for determining the deterioration by comparing the actual measurement value and the theoretical value of the parallel resistor R _p.

First, the theoretical value of the parallel resistor R _p. Parallel resistor R _p corresponds to the resistance value which is obtained from the slope of the DC-IV characteristics of a PN junction of the solar cell module. However, since the solar cell module is provided with a bypass diode, when measuring the impedance of the solar cell module, applying a reverse bias to the PN terminal turns on the bypass diode in a relatively small voltage range. Unable to get properties. Therefore, as described in the first embodiment, in measuring the impedance of the solar cell module, the DC bias Vdc is superimposed on the input AC signal. Furthermore, by making the amplitude of the AC signal sufficiently small, the applied voltage is kept at a positive value to prevent the bias diode from being turned on, and the slope of the DC-IV characteristic is also reduced by the diode characteristic of the solar cell module. It can be measured in a region that can be regarded as substantially constant. Such contrivance, can be regarded as equivalent parallel resistor R _p which is obtained from the impedance measured forward resistance R _F of the PN junction.

For example, p. The 119, theoretical methods for Determination of forward resistance R _F is described. In accordance with this method, it is possible to calculate the forward resistance R _F at any temperature for the DC bias Vdc. The values obtained by theory are not accurate enough to reproduce the measured values with sufficient accuracy, but the temperature dependence is generally reproduced. Therefore, in the present embodiment, the temperature dependency obtained from the theoretical value is used for determining the deterioration of the solar cell module. FIG. 17 is a diagram showing the temperature dependence of the theoretically obtained forward resistance _RF value ( _RF (T)) based on the forward resistance _RF value ( _RF (0)) at T = 0.degree. It is. Specifically, assuming a standard Si-doped solar cell using a phosphorus-doped p-type substrate, physical properties include a donor concentration of 1 × 10 ²¹ (1 / cm ³ ) and an acceptor concentration of 1 × 10 ¹⁶ (1 / cm ³ ). , Conduction state effective state density 2.8 × 10 ¹⁹ (1 / cm ³ ), valence band effective state density 2.65 × 10 ¹⁹ (1 / cm ³ ), electron mobility 120 (cm ² / Vs) , The lifetime of each of the electrons and holes is 1 ms, and the calculation is performed in consideration of the temperature dependence of the intrinsic semiconductor carrier density, the electron diffusion coefficient, the hole diffusion coefficient, the band gap, and the hole mobility. Other physical constants use well-known representative values.

Next, the parallel resistance _Rp is measured. After a certain period of time is passed while shielding the measurement target module from light, the temperature of the solar cell module is measured. In this embodiment, a non-contact type infrared laser thermometer is used, but a contact type measurement using a thermocouple or the like may be used. Then, the frequency spectrum of the impedance Z and the phase angle θ is measured for the solar cell module to be inspected as in the first embodiment. It converts the measured data into frequency spectrum of the parallel resistor R _p, obtaining the lowest frequency of the R _p values (R _p _low). As described in the first embodiment, R _p _low is the value of the circuit constant R _p independent of frequency. Therefore, the R _p value obtained from the temperature dependency of the forward resistance R _F theoretical values shown in the temperature T (° C.) and 17 measured, the R _p values calculated, in particular temperature at which the deterioration determination Convert to _Rp value. As shown in FIG. 17, in a relatively narrow temperature range of about 0 to 80 ° C., the vertical axis is logarithmically plotted, so that the temperature dependency can be regarded as substantially a straight line. For example, if the measured temperature is T ₁ (° C.) and the obtained R _p is R _p (T ₁ ), the R _p value (R _p (T)) at the temperature T (° C.) is obtained by the following equation. .
_{log [R p (T)]} = A × (T 1 -T) + log [R p (T 1)]
Here, A is the average slope of the temperature dependence shown in FIG. The R _p value obtained from data measured at any temperature this way can be converted into R _p value at a particular temperature.

As shown in Example 1, when comparing the temperature dependence of the normal module and the temperature dependency of the deteriorated module, as shown in FIG. 11, the difference between the two becomes small in the temperature range of 50 ° C. or more, and it is possible to determine the presence or absence of deterioration. It becomes difficult. Further, in order to change the value of the parallel resistor R _p in accordance with the degree of the module degradation, also changes the positional relationship of the normal module degradation module shown in FIG. 11. As the degree of deterioration becomes smaller, the line of the deteriorated module approaches the line of the normal module, so that the temperature range in which deterioration can be determined is narrowed. The temperature range is ultimately determined in consideration of the amount of deterioration to be detected, but it is safe to perform the measurement at a temperature of approximately 40 ° C. or less.

Determination of deterioration is carried out by converting the R _p values obtained experimentally certain temperature, for example, R _p value at 25 ° C., compared with a predetermined threshold value. The threshold value may be appropriately determined based on the degree of deterioration to be detected or a measurement error.

The system configuration for executing the second embodiment is the same as that of the first embodiment. Degradation evaluating portion 122b in the solar cell module diagnostic program is configured to perform the deterioration determination by converting the actually measured R _p values as described above in R _p values at a given temperature.

However, in the second embodiment, the deterioration determination can be greatly simplified. FIG. 18 shows a flowchart for determining whether or not the solar cell module has deteriorated. In the second embodiment, the parallel resistance _Rp value obtained from the lowest frequency impedance Z is used for the deterioration determination. Therefore, unlike the first embodiment, it is not necessary to acquire the frequency spectrum of the impedance Z, and the measurement can be significantly simplified as compared with the first embodiment. For example, a hand-held simple LCR meter cannot measure the impedance while continuously changing the frequency of the input signal, and thus cannot be used in the method of the first embodiment. In contrast, since it is Okonaere impedance measurement at a particular frequency which can be regarded as in Example 2, the phase angle θ is 0, obtains the R _p values at low frequencies using such simple LCR meter, a certain temperature , The deterioration diagnosis of the solar cell module becomes possible. That is, a simple diagnosis of a solar cell module can be performed by a simple LCR meter driven by a battery.

  First, with the solar cell module in a light-shielded state, an AC signal having a predetermined frequency at which the phase angle θ can be regarded as 0 is input and the impedance of the solar cell module is measured (S21). Further, the temperature when the impedance of the solar cell module is obtained is measured (S22).

Using the obtained impedance of the solar cell module, a parallel resistance R _p ′ constituting an equivalent circuit of the solar cell module in a light-shielded state is calculated (S23). At this time, since it can be considered that the phase angle θ = 0, it can be calculated as R _p ′ = | Z | according to (Equation 4) in FIG. Since the parallel resistance R _p ′ has a large temperature dependency as described above, the parallel resistance obtained in step S23 is converted into a parallel resistance at a predetermined temperature. Therefore, the solar cell evaluation apparatus 100 of Example 2 for converting the parallel resistor R _{p 'into} a parallel resistor R _p in a predetermined temperature, in advance holds the temperature dependency information of the forward resistance of the PN junction of the solar cell module ing. This temperature dependency information can be theoretically calculated based on the physical parameters of the solar cell as described above. Using this temperature dependency information, the parallel resistance R _p ′ is converted to a parallel resistance R _p at a predetermined temperature (S24), and the deterioration of the solar cell module is determined based on the parallel resistance R _p (S25 to S28). . For example, if the parallel resistance R _p exceeds the threshold value R _p _ref is determined that there is no deterioration, the parallel resistance R _p is determined that there is deterioration in the case of less than the threshold R _p _ref. As shown in FIG. 11, since the difference between the normal module and the deteriorated module increases as the module temperature decreases, it is desirable that the temperature at which the resistance value is compared be lower than the temperature at which impedance measurement is performed.

As described in Example 1, temperature dependency of the cutoff frequency fc of the parallel resistor R _p that are strongly correlated. Therefore, similarly to the deterioration determination by the parallel resistor R _p, it is also possible to perform the deterioration determination by the cut-off frequency fc.

10, 30, 70: equivalent circuit, 11: current source, 12: diode, 13: shunt resistance, 14: series resistance, 15: P terminal, 16: N terminal, 21, 40, 131 ... solar cell module, 22 ... String, 23 ... Array, 24 ... Connection box, 25 ... Power conditioner, 26 ... Insulation transformer, 27 ... System, 31, 71 ... Capacitance, 32, 72 ... Parallel resistance, 34 ... Inductance, 41 ... Sine wave oscillator, 42 current-voltage converter, 43 vector voltage ratio measurement unit, 51 bias power supply, 52 oscillator, 53 synthesis circuit, 54 reference resistance, 55 control amplifier, 56, 57 voltmeter, 58 ratio 100, solar cell evaluation device, 101, processor, 102, main memory, 103, auxiliary memory, 104, input / output interface, 105, display interface, 06 ... I / O port, 107 ... network interface, 108 ... Bus, 109 ... input device, 110 ... display, 120 ... measurement data, 122 ... solar cell module diagnostics, 130 ... measuring device.

Claims (17)

With the solar cell module in a light-shielded state, the frequency of the input AC signal is continuously changed to obtain a frequency spectrum of the impedance and the phase angle of the solar cell module,
From the obtained frequency spectrum of the impedance and phase angle of the solar cell module, calculate the frequency spectrum of the capacitance constituting the equivalent circuit of the solar cell module in the light-shielded state,
In the frequency spectrum of the capacitance of the solar cell module, the solar cell module by comparing the capacitance value on the lower frequency side than the cutoff frequency and the capacitance value on the higher frequency side than the cutoff frequency A method of diagnosing a solar cell module for diagnosing a solar cell module. In claim 1,
The method for diagnosing a solar cell module, wherein the cutoff frequency is a frequency at which a phase angle of the solar cell module is −45 °. In claim 2,
A method for diagnosing a solar cell module, wherein the frequency for giving the capacitance value on the high frequency side is a frequency of 100 kHz or less. In claim 3,
In the case where the frequency spectrum of the phase angle of the solar cell module does not reach −90 ° or more over a predetermined threshold value in a frequency range of 100 kHz or less, or when the cutoff frequency does not exist in the frequency range of 100 kHz or less. And a method for diagnosing a solar cell module that determines that the solar cell module is deteriorated. In claim 1,
As a capacitance value on the higher frequency side than the cutoff frequency, a predetermined value is assumed in advance,
A method for diagnosing a solar cell module, wherein a diagnosis of the solar cell module is performed by comparing a capacitance value on a lower frequency side than the cutoff frequency with the predetermined value. With the solar cell module in a light-shielded state, the frequency f of the input AC signal is continuously changed to obtain a frequency spectrum of the impedance Z and the phase angle θ of the solar cell module,
From the obtained frequency spectrum of the impedance Z and phase angle θ of the solar cell module, calculates the frequency spectrum of the capacitance C _p of the frequency f of the AC signal constitutes an equivalent circuit of the solar cell module of the light-shielding state in less than 100kHz And
Diagnosing the solar cell module based on the calculated frequency spectrum of the capacitance _Cp of the solar cell module,
The capacitance _{C p} of the solar cell module, -sinθ / 2πf | Z | diagnostic method of the solar cell module is calculated as. In claim 6,
In the frequency spectrum of the capacitance C _p of the solar cell module, the solar by comparing the capacitance value of the high-frequency side of the cut-off frequency and the capacitance value of the low-frequency side than the cut-off frequency A method of diagnosing a solar cell module for diagnosing a battery module. In claim 6,
In the frequency spectrum of the capacitance C _p of the solar cell module, the solar cell module for performing diagnosis of the solar cell module by comparing the capacitance values with a predetermined threshold value of the low-frequency side than the cut-off frequency Diagnostic method. In claim 7 or claim 8,
The method for diagnosing a solar cell module, wherein the cutoff frequency is a frequency at which a phase angle of the solar cell module is −45 °. In claim 9,
In the case where the frequency spectrum of the phase angle of the solar cell module does not reach −90 ° or more over a predetermined threshold value in a frequency range of 100 kHz or less, or when the cutoff frequency does not exist in the frequency range of 100 kHz or less. And a method for diagnosing a solar cell module that determines that the solar cell module is deteriorated. The temperature dependency information of the forward resistance of the PN junction of the solar cell module is held in advance,
With the solar cell module in a light-shielded state, an AC signal having a predetermined frequency is input to obtain the impedance Z of the solar cell module,
Measure the temperature when obtaining the impedance of the solar cell module,
Using an impedance Z of the acquired solar cell module calculates the parallel resistor R _p which constitutes an equivalent circuit of the solar cell module in the light shielding state,
Converting the calculated parallel resistance value of the solar cell module into a parallel resistance value at a predetermined temperature based on the temperature dependency information,
Diagnose the solar cell module based on the parallel resistance value of the solar cell module at the predetermined temperature,
The method for diagnosing a solar cell module, wherein the predetermined frequency is a frequency at which a phase angle of the solar cell module when the AC signal having the predetermined frequency is input can be regarded as 0. In claim 11,
The acquisition of the impedance of the solar cell module is performed at a temperature of 40 ° C. or less,
The method for diagnosing a solar cell module, wherein the predetermined temperature is lower than a temperature when the impedance of the solar cell module is acquired. In claim 11,
A method for diagnosing a solar cell module, wherein the parallel resistance _Rp is calculated as | Z |. A diagnostic device for a solar cell module,
A processor,
Memory and
The frequency spectrum of the impedance and the phase angle of the solar cell module obtained by continuously changing the frequency of the input AC signal while the solar cell module is in the light-shielded state is read into the memory, and is executed by the processor. An auxiliary memory for storing a solar cell module diagnostic program,
The solar cell module diagnostic program has a deterioration evaluation unit,
The deterioration evaluation unit is calculated from the frequency spectrum of the impedance and the phase angle of the solar cell module, the frequency spectrum of the capacitance constituting the equivalent circuit of the solar cell module in the light-shielded state, the frequency lower than the cutoff frequency A diagnostic device for a solar cell module that diagnoses the solar cell module by comparing the capacitance value on the side of the solar cell module with the capacitance value on the higher frequency side than the cutoff frequency. In claim 14,
The diagnostic device for a solar cell module, wherein the cutoff frequency is a frequency at which a phase angle of the solar cell module is −45 °. In claim 14,
The diagnostic device is connected to a measurement device connected to the solar cell module in a light-shielded state,
The solar cell module diagnostic program has an impedance measuring unit,
The diagnostic device for a solar cell module, wherein the impedance measuring unit sets a measurement parameter for the measuring device and acquires a frequency spectrum of the impedance and the phase angle of the solar cell module measured by the measuring device. In claim 14,
The deterioration evaluation unit, as a capacitance value on the higher frequency side than the cutoff frequency, a predetermined value is assumed in advance, and the capacitance value on the lower frequency side than the cutoff frequency and the predetermined value. A diagnostic device for a solar cell module that diagnoses the solar cell module by comparing.

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