Patent Application
20110068817
The present invention relates to a solar cell output characteristic evaluation apparatus and a solar cell output characteristic evaluation method including a forward bias power supply supplying an electronic load device for a solar cell output characteristic measurement.
In recent years, a large size and high capacity solar cell has been achieved, and a solar cell of which output current is 10 A or more and output voltage is 200 V or more has been manufactured. Performance of the solar cell when it receives solar light is evaluated by I-V characteristic of the solar cell.
An apparatus and a method using a variable resistor are popular as a measurement apparatus and a method evaluating the I-V characteristic of the solar cell, and the apparatuses and the methods using a capacitor load, a bias power supply, an electronic load as the variable resistor are known (refer to Non-Patent Document 1).
However, there are a problem in which a short-circuit current Isc cannot be measured accurately caused by a connecting wire resistance or the like in the above-stated respective I-V characteristic evaluation methods of the solar cell, and a problem in which an open-circuit voltage Voc cannot be accurately measured caused by an effect of a breaking current of a transistor or the like in the above-stated method using the electronic load.
The present inventors invented a capacitor load type solar cell I-V curve tracer including a reverse bias circuit applying an electric potential with reversed polarity of an output of the solar cell in Patent Document 1.
Solar cell measurement system (a° Instruments Co., Ltd. Homepage)
Japanese Patent Application Publication No. Hei 2-159588
However, there has been a problem in which the short-circuit current Isc can be measured accurately because the reverse bias circuit is provided, but the open-circuit voltage Voc cannot be measured accurately because there isn't a forward bias function when the I-V characteristic evaluation of the solar cell is performed by using the capacitor load type solar cell I-V curve tracer described in the above-stated Patent Document 1.
Besides, a power supply called as a bipolar power supply is used in the above-stated bias power supply type I-V characteristic evaluation of the solar cell, and a bipolar application is possible for both current and voltage.
However, a supply and receive power capacity capable of sustaining electric power of a solar cell being a measurement object is required for the power supply used for the I-V characteristic evaluation of the solar cell, and therefore, a cost increasing resulting from large size becomes a problem in the high capacity bipolar power supply discharging a large current.
In consideration of the above-stated problems, an object of the present invention is to provide a solar cell output characteristic evaluation apparatus and a method thereof capable of accurately measuring the open-circuit voltage Voc by applying the forward bias current with a minimum power consumption without requiring the bipolar power supply discharging/absorbing the large current causing a cost increase.
According to the present invention, a solar cell output characteristic evaluation apparatus measuring output characteristic of a solar cell, including: a solar cell; a voltmeter measuring a voltage of the solar cell; an ammeter measuring a current value flowing in the solar cell; a variable resistor part connected to the solar cell; a forward bias circuit connected to the solar cell; and a reverse bias circuit connected to the solar cell, is provided.
The variable resistor part may be made up of an electronic load control circuit and a load power semiconductor.
The forward bias circuit may be made up of a forward bias resistor, a forward bias power supply and a forward bias parasitic current compensation circuit.
The variable resistor part and the reverse bias circuit are included in a power conversion circuit with reverse bias, and the power conversion circuit with reverse bias may be made up of a switching transformer, a backflow preventing diode, a reverse bias stabilizing capacitor and a load circuit.
Besides, according to another aspect of the present invention, a solar cell output characteristic evaluation method in which a voltmeter, an ammeter and an electronic load being a variable resistor are connected to a solar cell, and current-voltage characteristic of the solar cell are obtained by changing the electronic load, including: applying a reverse bias voltage in reverse of an output of the solar cell; applying a forward bias voltage to the solar cell; and measuring a short-circuit current and an open-circuit voltage of the solar cell is provided.
In the applying the forward bias voltage, a function restricting a maximum output voltage may be added to the forward bias power supply.
A high capacity electronic load device using a switching system may be used as the variable resistor.
A noise component may be removed from an output voltage, an output current obtained from the solar cell, and actual measured values of a monitor cell by using known characteristic.
According to the present invention, a solar cell output characteristic evaluation apparatus and a method thereof capable of accurately measuring an open-circuit voltage Voc by applying a forward bias current with a minimum power consumption without requiring a bipolar power supply discharging/absorbing a large current causing a cost increase are provided.
Hereinafter, embodiments of the present invention are described with reference to the drawings. Note that the same reference numerals and symbols are added to components having substantially the same function, and redundant description thereof is not given in the specification and the drawings.
At first, a conventional solar cell I-V curve tracer is described below.
Besides,
In the solar cell I-V curve tracer 100 illustrated in
Accordingly, the reverse bias circuit 10 illustrated in
On the other hand, it is impossible to accurately measure the open-circuit voltage Voc because the output current of the solar cell 1 does not become “0” (zero) A resulting from a characteristic of the variable resistor part 30 and it is just lowered to a certain current (a point “c” in
A solar cell output characteristic evaluation apparatus 50 according to an embodiment of the present invention described below is therefore proposed.
The voltmeter 2 measuring the output voltage and the ammeter 3 measuring the output current are connected to the solar cell 1. Besides, the variable resistor part 30 and the reverse bias circuit 10 are connected at downstream of the ammeter 3 as same as the solar cell I-V curve tracer 100. Here, the variable resistor part 30 is made up of a load power semiconductor 33 being, for example, an HFET (Hetero structure Field Effect Transistor) and an electronic load control circuit 35. Further, a forward bias circuit 60 is connected at downstream of the ammeter 3 so as to be in parallel with the variable resistor part 30 and the reverse bias circuit 10 relative to the solar cell 1. Here, a constitution of the reverse bias circuit 10 is as same as the above-stated I-V curve tracer. A constitution of the forward bias circuit 60 is the one in which a forward bias resistor 62, a forward bias power supply 64, and a forward bias parasitic current compensation circuit 66 are connected from a circuit upstream side. A downstream side of the forward bias circuit 60 is connected to the reverse bias circuit 10, and between the forward bias power supply 64 and the forward bias parasitic current compensation circuit 66 inside the forward bias circuit 60 and between the variable resistor 30 and the reverse bias circuit 10 are connected.
Hereinafter, a process measuring the I-V characteristic by using the solar cell output characteristic evaluation apparatus 50 according to a first embodiment constituted as illustrated in
The constitutions of respective parts in
Just before the I-V characteristic measurement is performed, a charge is performed for the reverse bias stabilizing capacitor 24 by the reverse bias power supply 20 with a reverse polarity of the output of the solar cell 1 in the reverse bias circuit 10 as represented by a dotted line 70 in
A reverse bias voltage is applied to the solar cell 1 by an electric charge voltage charged to the reverse bias stabilizing capacitor 24 when the characteristic measurement is started. At this time, a value at the point “a” in
After that, a control to enlarge a load resistance value of the solar cell 1 is performed by the load power semiconductor 33 controlled by the electronic load control circuit 35, and the voltage charged to the reverse bias stabilizing capacitor 24 is rapidly discharged. At this time, a voltage in reverse direction is applied to the reverse bias stabilizing capacitor 24, but the voltage in reverse direction is not applied to the reverse bias stabilizing capacitor 24 because the voltage in reverse direction is clamped to a forward direction voltage of the backflow preventing diode 22 owing to an effect of the backflow preventing diode 22.
The value of the voltmeter 2 changes from the point “a” to the point “b” during the above-stated process. A change of value of the ammeter 3 in accordance with the change of the value of the voltmeter 2 is measured, and thereby, it becomes possible to accurately obtain the short-circuit current Isc being the value of the ammeter 3 when the voltage of the solar cell 1 is set at “0” (zero) V. Note that, at this time, the forward bias current 74 from the forward bias circuit 60 does not flow toward the solar cell 1 but flows toward the load power semiconductor 33 because a resistance value of the variable resistor 30 is small. The forward bias current 74 returns to the forward bias power supply 64 via the load power semiconductor 33.
Besides,
The constitutions of respective parts in
A control to enlarge the load resistance value of the solar cell 1 is performed by the load power semiconductor 33 controlled by the electronic load control circuit 35, and the current does not flow toward the load power semiconductor 33. At this time, the current measured by the ammeter 3 changes from the point “c” to a point “d” in
Here, the forward bias current 74 flows into the solar cell 1 and stored at the reverse bias stabilizing capacitor 24 as illustrated in
It becomes possible to perform more accurate evaluation as for the I-V characteristic of the solar cell 1 by accurately measuring the short-circuit current Isc and the open-circuit voltage Voc through the process measuring the I-V characteristic by using the solar cell output characteristic evaluation apparatus 50 as stated above.
Hereinabove, an example of the embodiment of the present invention is described, but the present invention is not limited to the illustrated embodiment. It is obvious that those skilled in the art are able to figure out various changed examples or modified examples within the range of the following claims, and it is to be understood that all those changes and modifications are to be included in the technical scope of the present invention.
For example, it is preferable that a restricting function capable of restricting a maximum output voltage of the forward bias power supply 64 in the forward bias circuit 60 is to be added to perform the evaluation of various solar cells by the same solar cell output characteristic evaluation apparatus.
A small-size and low capacity solar cell is also manufactured while a large-size and high capacity solar cell has been enabled. When the I-V characteristic measurement is performed by the solar cell output characteristic evaluation apparatus 50 described in the above-stated embodiment in the small-size solar cell, an overvoltage is applied to the solar cell 1 caused by the voltage from the forward bias power supply 64 inside the forward bias circuit 60, and there is a possibility that the solar cell 1 is broken. Accordingly, it is conceivable to enable to control the maximum output voltage so that the output voltage from the forward bias power supply 64 becomes an adequate voltage corresponding to the small-size solar cell and so on.
Besides, when the output voltage and the output current output from the solar cell 1 are output over ratings of the voltmeter 2 and the ammeter 3, it may cause troubles or the like of the voltmeter 2, the ammeter 3 and the load power semiconductor 33. Accordingly, it is also conceivable that observed values of the voltmeter 2 and the ammeter 3 are monitored at the electronic load control circuit 35, comparisons between respective observed values and the rated values of the voltmeter 2 and the ammeter 3 are performed, and it is controlled so that the observed values of the voltmeter 2 and the ammeter 3 do not exceed the rated values by controlling the load power semiconductor 33 when the observed value exceeds the rated value in the comparison.
It is also conceivable that a high capacity electronic load device using a switching system is used as the reverse bias circuit in the above-stated embodiment to accurately obtain the short-circuit current Isc.
A high capacity electronic load device 90 using the switching system is described below with reference to the drawings.
The switching system means that a rate of turning ON/OFF of an electronic switch is changed effectively to control electric power to the load. The load switching circuit 85 using the switching system is a load when it is seen from a power supply side, and it is possible to artificially lower the load of the solar cell 1 from the infinite while regarding the switching power load as an electronic load. However, an extremely low resistance value of the solar cell 1 cannot be achieved by using only the load switching circuit 85 using the switching system, and the short-circuit current Isc cannot be accurately measured.
A reverse bias circuit corresponding to the switching system is therefore provided to obtain the short-circuit current Isc. The process is described below.
Just before the I-V characteristic measurement is performed, the current does not flow in the switching transformer 82, and therefore, the reverse bias stabilizing capacitor 87 is not charged.
After that, the load switching circuit 85 is controlled by the electronic load control circuit 35 so that the load resistance value of the solar cell 1 is to be the minimum from the infinite when the I-V characteristic measurement is started. At this time, the load resistance value of the solar cell 1 gradually decreases from the infinite, and therefore, the solar cell output current 72 flows. A voltage is applied to the switching transformer 82 by the solar cell output current 72, and the charge with the reverse polarity of the output of the solar cell 1 is performed to the reverse bias stabilizing capacitor 87.
When the load resistance value of the solar cell 1 approximates to the minimum, the output voltage of the solar cell 1 approximates to “0” (zero) V, and the reverse bias is applied to the solar cell 1 caused by the electric charge voltage charged to the reverse bias stabilizing capacitor 87. At this time, the value at the point “b” in
When the load resistance value of the solar cell 1 becomes “0” (zero), the reverse bias is applied to the solar cell 1 caused by the electric charge voltage charged to the reverse bias stabilizing capacitor 87. Accordingly, the value at the point “a” in
The value of the voltmeter 2 changes from the point “b” to the point “a” in
Besides, the open-circuit voltage Voc when the output current of the solar cell 1 is set at “0” (zero) A can be obtained accurately by using the forward bias circuit 60 having the similar constitution as the above-stated embodiment in the high capacity electronic load device 90 using the switching system. The process thereof is the same as the above-stated embodiment, and therefore, the description is not given.
On the other hand, it is generally known that a noise component is contained in measurement data of the I-V characteristic measurement of the solar cell depending on a measurement environment. It is also conceivable that a method removing the noise component from the obtained measurement data is applied to, the present invention to perform the more accurate I-V characteristic measurement of the solar cell. A characteristic function representing the characteristic thereof is well known in the solar cell, and a result to be obtained can be expected. The noise component can be removed from each measurement data based on expected information. Removal of the noise component is described below.
The solar cell I-V characteristic measurement data measured by an electronic load device are the output voltage of the solar cell, the output current of the solar cell, actual measurement values of a monitor cell, and so on. Note that the monitor cell is a cell of which conversion factor is accurately measured in advance, and of which relationship between the output current and light intensity is obvious.
Parameters are determined so that each measurement data most approximates to a known function as for each measurement data. Here, the known function is a function having theoretical and principle validity, and a polynomial approximation, a learning result of a neuro-computer, a table search, and so on are conceivable as for the parameter determination.
For example, when a quadratic expression approximation is applied as the known function, coefficients “a”, “b”, “c” in “y=ax2+bx+c” are found from the measurement data. It becomes possible to accurately obtain the solar cell output voltage, the solar cell output current from the parameters by using the quadratic expression determined by the found coefficients “a”, “b”,
According to this method, values of Isc, Voc, Pmax, Vpm, Ipm, FF, EFF, and so on can be found by a calculation from the found coefficients.
Besides, conventionally, the data as for the I-V characteristic in every case should be stored to reproduce the measurement data, but only the obtained parameters are to be stored in this method.
It is desirable to perform more accurate light intensity correction as for the output of the solar cell of which noise component is removed.
In the characteristic evaluation of the solar cell, the light intensity decreases as time passes when a flash lamp is used. Accordingly, the light intensity correction is required for the output of the solar cell. Hereinafter, it is described that the light intensity is corrected such that an irradiance is measured at 1000±50 W/m2.
At first, before the light intensity correction is performed, the measurement is performed in a time zone when adequate light intensity is output by the output current of the monitor cell. Here, it is the time zone when the irradiance is at 1000±50 W/m2. The I-V characteristic measurement of the solar cell is performed at this time zone. In this case, the time zone when the light intensity is output correctly is short, and therefore, the measurements are performed for plural times while shifting timings to start the I-V characteristic measurements. A measurement voltage is sequentially increased from a short-circuit state to the open-circuit voltage Voc for the data measured when the adequate light intensity is output.
Next, the light intensity correction of the output current of the solar cell is performed. In this case, a value of the light intensity is ±5% or less, and therefore, the light intensity correction of the output current of the solar cell may be performed by using a proportional correction. The solar cell I-V characteristic is created based on the data obtained by the above-stated measurements. Note that the solar cell I-V characteristic created here is called as a reference curve.
The solar cell I-V characteristic measurement of a new solar cell with the same characteristic is performed within a range of the light intensity of ±20%. Here, the measurement is performed once, and the noise removal is performed as for the measurement data. The light intensity correction of the output current of the solar cell is performed by using the obtained data. The output current of the solar cell is represented by the following expression, but this expression is a nonlinear type, and therefore, an analytic light intensity correction is difficult.
The light intensity correction of the output current of the solar cell is performed based on the following expression. Namely, an output current value “in” of the solar cell is found by using a proceeding current value “in−1”.
Further, a table capable of setting appropriate values for each is prepared in advance as for the diode factor nd, the series resistance rs of the solar cell, the parallel resistance rsh of the solar cell. The I-V characteristic of the solar cell is obtained based on the values set at the table.
Here, the solar cell I-V characteristic with the most consistency, having the consistency with the solar cell I-V characteristic called as the reference curve is to be determined in advance to judge which parameter is appropriate. After that, the parameters are applied and calculated to the measurement result.
The present invention is applicable for a solar cell output characteristic evaluation apparatus and a solar cell output characteristic evaluation method including a forward bias power supply supplying to an electronic load device for a solar cell output characteristic measurement.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-136771 | May 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/059528 | 5/25/2009 | WO | 00 | 11/24/2010 |
