Patent Publication Number: US-2011069479-A1

Title: Pseudo solar light generation apparatus and pseudo solar light generation method for solar cell characteristic measurement

Description:
TECHNICAL FIELD 
     The present invention relates to a pseudo solar light generation apparatus and a pseudo solar light generation method for a solar cell characteristic measurement. 
     BACKGROUND 
     Conventionally, a method in which pseudo solar light is irradiated and I-V characteristic of a solar cell at that time are measured has been taken in a solar cell I-V characteristic measurement. 
       FIG. 1  is an explanatory view illustrating a conventionally used direct-current lighting discharge lamp lighting device  100  (refer to Non-Patent Document 1). As illustrated in  FIG. 1 , the direct-current lighting discharge lamp lighting device  100  is made up of a lamp, an igniter starting (dielectric breakdown) the lamp and performing a transition to an arc discharge, and a lighting device controlling a lamp current to maintain the arc discharge. 
     Besides,  FIG. 2  is a graphic chart representing a relationship between elapsed time and the lamp current and a lamp voltage. In  FIG. 2 , the time until the lamp current and the lamp voltage become stable is the transition to the arc discharge, and the time when both of them are stable is the maintenance of the arc discharge. 
     A solar cell I-V characteristic measurement is performed while the lamp maintains the arc discharge, and therefore, the time when the are discharge is maintained is preferable to be long. 
     Note that a series pass (dropper) system capable of high-speed response is used as the lighting device controlling the lamp current, and a switching system capable of expecting a small-sizing and light-weighting is not much used because a response characteristic thereof is not enough and it is difficult to increase electric power. 
     [Non-Patent Document 1] 
     Optical Technology Information Magazine “Light Edge” No. 15 Special Issue, Discharge Lamp (published November, 1998) 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, when a commercial power supply is set at a predetermined voltage by a transformer, the voltage is rectified by a diode, and used as a direct-current by a smoothing capacitor in an I-V characteristic measurement of a large-sized solar cell developed in recent years a circuit scale becomes large-sized to correspond to an instant large power. 
     Besides, in recent years, a high-efficiency solar cell has been invented and developed in which an I-V characteristic measurement performance taking several hundred milli-second for measurement is required. There has been a problem in which capacity of a capacitor is small and the time maintaining the arc discharge becomes very short by using a conventional flash discharge lamp as a solar light generation apparatus corresponding to the I-V characteristic measurement of the high-efficiency solar cell. Accordingly, it is conceivable to lengthen the time for maintaining the arc discharge by enlarging the capacity of the capacitor storing electric power, but it is not practical because the circuit scale of the lighting device becomes large. 
     Further, there has been a problem in the flash discharge lamp in which irradiance necessary for the I-V characteristic measurement is not constant because the irradiance changes largely as time goes, and as a result, an accurate measurement of the high-efficiency solar cell cannot be performed. 
     In consideration of the above-stated problems, an object of the present invention is to provide a pseudo solar light generation apparatus and a pseudo solar light generation method capable of increasing electric power, performing the accurate I-V characteristic measurement of the high-efficiency solar cell, and lengthening the time for maintaining the arc discharge of the lamp while using the switching type power supply system. 
     Means for Solving the Problems 
     According to the present invention, a pseudo solar light generation apparatus for a solar cell characteristic measurement, including: a flash lamp; a switching type boosting power supply circuit; a light emitting intensity detection sensor; a charging power supply; a control circuit controlling a charge and discharge, a voltage, a current and light intensity; a current detector; a class D amplifier circuit; an amplifier output control circuit; and an electric double layer capacitor and power control circuit, is provided. 
     The light emitting intensity detection sensor may be a spectral sensitivity sensor of which spectral sensitivity is equal to that of a solar cell being a measurement object. 
     The flash lamp may include a reflective mirror, a condenser, and an optical fiber connected to the condenser. 
     According to another aspect of the present invention, a pseudo solar light generation method for a solar cell characteristic measurement, including: performing a charge of an electric double layer capacitor by a charging power supply; lighting a flash lamp by a discharge from the electric double layer capacitor; performing a constant current control of a current at a current detector by a control circuit controlling a charge and discharge, a voltage, a current and light intensity; controlling the light intensity of the flash lamp to a target amount by the control circuit; and finishing the lighting of the flash lamp by terminating the discharge from the electric double layer capacitor after a predetermined time passed, is provided. 
     EFFECT OF THE INVENTION 
     According to the present invention, a pseudo solar light generation apparatus capable of increasing electric power, performing an accurate I-V characteristic measurement of a high-efficiency solar cell, and lengthening a time for maintaining an arc discharge of a lamp while using a switching type power supply system is provided. 
     Namely, a high-capacity electric double layer capacitor is used for a lighting device for a pseudo solar light generation, and thereby, it is possible to downsize a power supply. Besides, the electric double layer capacitor having a large storage capacity is used, and thereby, it becomes possible to extend a lighting time of the lighting device which has been conventionally short, up to a necessary and sufficient time. 
     Further, a negative feedback control is smoothly performed and irradiance is stabilized by applying the negative feedback control and a class D amplifier system used in continuous lighting for illuminance at the lighting time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is an explanatory view illustrating a direct-current lighting discharge lamp lighting device  100 . 
         FIG. 2  is a graphic chart representing a relationship between elapsed time and a lamp current and a lamp voltage. 
         FIG. 3  is an explanatory view of a pseudo solar light generation apparatus  1 . 
         FIG. 4  is an explanatory view explaining a configuration of a class D amplifier circuit  40 . 
         FIG. 5  is an explanatory view explaining an embodiment when a low reflectance dielectric mirror  92  and a convex surface reflective condenser lens  94  are provided. 
         FIG. 6  is an explanatory view of a light intensity detection method using an optical fiber. 
     
    
    
     EXPLANATION OF CODES 
     
         
           1  pseudo solar light generation apparatus 
           11  commercial power supply 
           12  charging power supply 
           20  electric double layer capacitor and power control circuit 
           30  switching type boosting power supply circuit 
           32  boosting inductor 
           34  backflow preventing diode 
           36  switching element 
           38  load smoothing capacitor 
           40  class D amplifier circuit 
           45  amplifier output control circuit 
           50  flash lamp 
           60  current detector 
           70  control circuit 
           80  light emitting intensity detection sensor 
           90  solar cell 
           100  direct-current lighting discharge lamp lighting device 
           110  reflective condenser mirror 
           120  optical fiber 
           125  fiber light receiver 
           200  light 
           202  light flux 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     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 in the specification and the drawings, and redundant description thereof is not given. 
       FIG. 3  is an explanatory view of a pseudo solar light generation apparatus  1  for solar cell characteristic measurement according to the embodiment of the present invention. 
     As illustrated in  FIG. 3 , the pseudo solar light generation apparatus  1  is made up of a commercial power supply  11 , a charging power supply  12 , an electric double layer capacitor and power control circuit  20 , a switching type boosting power supply circuit  30 , a class D amplifier circuit  40 , an amplifier output control circuit  45 , a flash lamp  50 , a current detector  60 , a control circuit  70 , and a light emitting intensity detection sensor  80 . 
     Here, the switching type boosting power supply circuit  30  is made up of a boosting inductor  32 , a backflow preventing diode  34 , a switching element  36 , and a load smoothing capacitor  38 . Besides, the control circuit  70  is a circuit controlling a charge and discharge, a voltage, a current, and light intensity. 
     Hereinafter, a constitution of the pseudo solar light generation apparatus  1  is described. 
     The commercial power supply  11  is connected to the charging power supply  12 , and the charging power supply  12  is connected to the electric double layer capacitor and power control circuit  20 . The flash lamp  50  is connected to the electric double layer capacitor and power control circuit  20 , and it is lighted when the current flows. Here, the switching type boosting power supply circuit  30 , the class D amplifier circuit  40 , and the current detector  60  are provided on an electric circuit to light the flash lamp  50 . Note that the class D amplifier circuit  40  is provided at upstream side (or at downstream side) of the flash lamp  50 , the current detector  60  is provided at downstream side (or at upstream side) of the flash lamp  50  respectively, and the switching type boosting power supply circuit  30  is provided to be connected to an upstream side and a downstream side of the electric double layer capacitor and power control circuit  20 . 
     Besides, the control circuit  70  performs a charge control of the charging power supply  12 , a discharge control of the electric double layer capacitor and power control circuit  20 , and a control of the switching type boosting power supply circuit  30 . On the other hand, the amplifier output control circuit  45  has a constitution controlling the class D amplifier circuit  40  by a voltage value output from the electric double layer capacitor and power control circuit  20 , a voltage value output from the switching type boosting power supply circuit  30 , a voltage value of the flash lamp  50 , and light intensity information output from the light emitting intensity detection sensor  80 . Note that the present invention relates to a case when the flash lamp  50  is lighted, namely, when the flash lamp  50  performs a maintenance of an arc discharge, and therefore, an igniter (flash lamp lighting trigger circuit) performing a transition to the arc discharge is not illustrated in the drawing. 
     Pseudo solar light is generated as described below in the pseudo solar light generation apparatus  1  constituted as stated above. 
     At first, electric power is supplied from the charging power supply  12  connected to the commercial power supply  11  to the electric double layer capacitor and power control circuit  20  and a charge is performed by the charge control of the control circuit  70 . After the charge of the electric double layer capacitor and power control circuit  20  is finished, the switching type boosting power supply circuit  30  is controlled by the control circuit  70 , a predetermined voltage is stored at the load smoothing capacitor  38 , and a lighting preparation of the flash lamp  50  is finished. 
     After the lighting of the flash lamp  50  is started, a state of the flash lamp  50  shifts from the transition to the arc discharge by the not-illustrated igniter to the maintenance of the arc discharge. Here, the shift to the maintenance of the arc discharge is performed by the current discharged from the electric double layer capacitor and power control circuit  20  by the control of the control circuit  70 . Further, a measurement value of the current detector  60  measuring a current value supplied to the flash lamp  50  is measured as needed to continue the maintenance of the arc discharge. When the current measurement value received by the control circuit  70  is lowered, the current flowing to the flash lamp  50  is increased by controlling the switching element  36  by the control circuit  70  to perform the control to keep a constant current. Note that the class D amplifier circuit  40  is provided between the switching type boosting power supply circuit  30  and the flash lamp  50  so as to correspond to a transient response in the present embodiment. 
     Besides, the control circuit  70  receives the light intensity information from the light emitting intensity detection sensor  80 , and performs a control to keep the light intensity of the flash lamp  50  constant by controlling the switching element  36  when it is judged that the light intensity of the flash lamp  50  is low from the light intensity information. 
     Here, a value of the constant current in the above-stated constant current control by the control circuit  70  is defined in the light intensity control so that the light intensity of the flash lamp  50  becomes a predetermined light intensity. 
     The flash lamp  50  is lighted for a predetermined time during a period when the maintenance of the arc discharge continues, the power supply from the electric double layer capacitor and power control circuit  20  is stopped by the control circuit  70  after the predetermined time has passed, and the lighting of the flash lamp  50  is finished in the above-stated process. When the flash lamp  50  is lighted, the solar cell characteristic measurement is performed. After that, the solar cell characteristic measurement is performed again by repeating the above-stated process again. 
     Here, the class D amplifier circuit  40  is described below with reference to the drawings. The class D amplifier circuit  40  provided at upstream of the flash lamp  50  (at downstream of the switching type boosting power supply circuit  30 ) is provided as a countermeasure against a slow transient response of a switching type power supply. 
     In general, the switching type power supply is used for a usage of which transient characteristic does not become an issue. There is a possibility in which an electric charge of the load smoothing capacitor  38  of the switching type boosting power supply circuit  30  flows into the flash lamp  50  (load), and an excessive current flows because of the slow transient response of the switching type power supply, when the class D amplifier circuit  40  is not provided although a large power operation is required in the present embodiment. An increase of the voltage becomes slow at a constant current operation time because a load voltage changes from a low state to a high state (load impedance increases). Besides, an excessive voltage occurs when the load current decreases rapidly at a constant voltage operation time. Further, there is a possibility in which large energy at a transient time breaks down or deteriorates the load, or makes the load unstable. 
     In the present embodiment, the class D amplifier circuit  40  is therefore provided between the switching type boosting power supply circuit  30  and the flash lamp  50  (load) to correspond to the transient response as illustrated in  FIG. 3 . Besides, the amplifier output control circuit  45  controlling an output of the class D amplifier circuit  40  is provided in accordance with the provision of the class D amplifier circuit  40 . 
       FIG. 4  is an explanatory view explaining a constitution of the class D amplifier circuit  40 . As illustrated in  FIG. 4 , the class D amplifier circuit  40  is made up of a gate-drive amplifier  42  and two MOSFETs  43 . 
     The class D amplifier circuit  40  inputs the voltage output from the switching type boosting power supply circuit  30 , and controls the voltage to the flash lamp  50  in accordance with the control of the amplifier output control circuit  45  to solve the above-stated problems. 
     Here, the amplifier output control circuit  45  is a circuit controlling the output of the class D amplifier circuit  40  so as not to apply the excessive current and the excessive voltage to the flash lamp  50  (load), and it can also be constituted by a microprocessor such as a generally known digital signal processor. As a concrete control thereof, the transient response is estimated from the voltage value output from the electric double layer capacitor and power control circuit  20 , the voltage value output from the switching type boosting power supply circuit  30 , the voltage value of the flash lamp  50 , and the light intensity information output from the light emitting intensity detection sensor  80 , to control the output of the class D amplifier circuit  40 . 
     The amplifier output control circuit  45  has a partial responsibility for the transient response of the switching type power supply, and thereby, it becomes possible to minimize power consumption of the class D amplifier circuit  40  and to use the switching type power supply without taking any consideration for the transient characteristic thereof. 
     It is possible to prevent an inrush current to the load caused by the electric charge of the load smoothing capacitor  38  by adding a discharging and absorbing constant current characteristic to the class D amplifier circuit  40  and to suppress an overshoot owing to the current absorbing characteristic. It is possible to set the load smoothing capacitor  38  at an object maximum voltage, and to perform a stable control by the class D amplifier circuit  40  with absorbing  1 ,  2 ,  3  quadrant types constant voltage constant current characteristic. 
     Load fluctuation and a response thereof are nonlinear states, and a DSP and so on is used to control response characteristic optimally by predictively controlling the transient response in a digital, manner because an object characteristic is not attained by an analog control method. 
     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, the switching type boosting power supply circuit  30  is controlled by the current supplied to the flash lamp  50  and the value of the light intensity of the flash lamp  50 , to control the light intensity of the flash lamp  50  to be constant in the above-stated embodiment. 
     However, the irradiance of the light of the flash lamp  50  is not in proportion at whole irradiation area. This is because the light emitting intensity detection sensor  80  detects only a part of the irradiated light of the flash lamp  50 . Accordingly, it is more desirable that all of the light intensity is controlled by signals in proportion to the light intensity at the whole irradiation area of the flash lamp  50  to further enhance the stability of the irradiance in the above-stated embodiment of the present invention. 
       FIG. 5  is an explanatory view explaining a case when a low reflectance mirror  92  and a condenser lens  94  are provided in the above-stated embodiment. At this time, the low reflectance mirror  92  is, for example, a surface reflecting mirror. 
     As illustrated in  FIG. 5 , the low reflectance mirror  92  is provided between the flash lamp  50  and a solar cell  90 , and the condenser lens  94  is provided between the low reflectance mirror  92  and the light emitting intensity detection sensor  80 . 
     The light at the whole irradiation area irradiated from the flash lamp  50  is reflected by the low reflectance mirror  92 , condensed by the condenser lens  94 , and of which light intensity is detected by the light emitting intensity detection sensor  80 . The detected light intensity information is transmitted to the control circuit  70 , and the light intensity of the flash lamp  50  is controlled to be constant based on the light intensity information. 
     Particularly, in case of a solar simulator in which a whole is uniformized by using an integral lens or the like, an effect to perform the light intensity detection by using the light at the whole irradiation area is large because there is a local small fluctuation. 
     A spectral distribution of the flash lamp  50  fluctuates as time goes. This fluctuation cannot be stabilized by a negative feedback at the whole area. Accordingly, there is a possibility in which fluctuation occurs in the solar cell output. It is preferable that a spectral sensitivity at the time of the light intensity detection and a spectral sensitivity of a measurement object (here, the solar cell  90 ) are made approximately equal, to minimize an effect of the spectral fluctuation by applying the negative feedback. 
     As a concrete method thereof, it is conceivable that a spectral sensitivity sensor having the spectral sensitivity similar to the solar cell  90  is used instead of the light emitting intensity detection sensor  80  in the above-stated embodiment. In this case, it becomes possible to minimize the effect of the spectral fluctuation because the spectral distributions of both are approximately the same. 
     Besides, it is also conceivable to provide a filter to equalize the spectral distribution of the light detected at the light emitting intensity detection sensor  80  with the spectral distribution of the solar cell  90  at a detection part of the light emitting intensity detection sensor  80  in the above-stated embodiment. In this case, it becomes possible to minimize the effect of the spectral fluctuation because the light emitting intensity detection sensor  80  detects the light intensity only within a range of the same spectral with the spectral distribution of the solar cell  90  via the filter. 
     On the other hand, the light emitted from the flash lamp  50  is optically guided to the irradiation area by using reflection and refraction. Accordingly, light flux which is difficult to be guided to the irradiation area is wasted. It is therefore desirable to guide the light flux to be wasted to the irradiation area by changing an optical path thereof by condensing the light flux to an optical fiber. It is described below with reference to the drawings. 
       FIG. 6  is an explanatory view of a light intensity detection method using the optical fiber. A reflective condenser mirror  110  is provided between the flash lamp  50  and the solar cell  90 , and a fiber light receiver  125  to which the optical fiber  120  is connected is provided at an opposite side of the reflective condenser mirror  110  relative to the flash lamp  50 . Note that a center portion of the reflective condenser mirror  110  has a structure transmitting the light of the flash lamp  50 , and a tip output direction of the optical fiber is a direction of the solar cell  90 . 
     Irradiation of light  200  (dotted arrows in  FIG. 6 ) heading from the flash lamp  50  to the solar cell  90  is the same as the above-stated embodiment. On the other hand, light flux  202  (dashed arrows in  FIG. 6 ) which is difficult to guide to the irradiation area from the flash lamp  50  is reflected by the reflective condenser mirror  110 , and the light flux  202  is condensed to a fiber light receiver  125 . The optical fiber  120  is connected to the fiber light receiver  125 , and the condensed light is output from a tip portion of the optical fiber  120 . The direction of the light output from the optical fiber  120  can be controlled, and the light is irradiated toward a portion where an irradiation light intensity is low at the solar cell  90 . 
     Accordingly, it becomes possible to improve a local lack of uniformity of the irradiation illuminance of the light from the flash lamp  50  relative to the solar cell  90 . 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a pseudo solar light generation apparatus and a pseudo solar light generation method for a solar cell characteristic measurement.