CN86101321A - Short pulse test equipment of solar cells technical scheme - Google Patents

Abstract

At present, the solar cell testing device using long-arc pulsed xenon lamp as the testing light source has complex structure, large volume and high price. In this program, the ten-thousand-time flashlight for photography or similar short-pulse lights (light pulse duration less than milliseconds) is used as a test light source. First, measure the dark characteristics and series resistance of the solar cell, and then determine the volt-ampere of the solar cell under light. characteristics, and then obtain various electrical performance parameters. This solution has simple structure, low power consumption, small size, easy to carry, low cost, the test area can be larger than several square meters, and can be used indoors or in the field.

Description

Technical solution for short pulse solar cell testing device

The present invention relates to a solar cell (single solar cell and various types of combined panels) electrical performance testing device, which can measure the volt-ampere characteristics of the solar cell and further obtain various electrical performance parameters.

Modern solar cell testing equipment consists of a complete set or supporting components, including a solar simulator, an electronic load, and a microcomputer data processing system. Solar simulators are available in two types: steady-state and pulsed. Steady-state solar simulators maintain constant irradiance and can be used with relatively simple microcomputer data processing systems. However, their main drawback is that they are difficult to apply to large-area solar cell panels. The average power consumption per square meter of the panel is difficult to measure below tens of kilowatts, resulting in bulky and expensive equipment. Another drawback is that continuous sunlight can cause solar cell temperatures to rise sharply.

Pulsed solar simulators overcome these two shortcomings to a certain extent. They use a stroboscopic pulse lamp (long-arc pulsed xenon lamp) as the test light source, with an instantaneous power of tens of kilowatts and an average power of only one-tenth of that. Each light pulse lasts on the order of milliseconds. Each flash measures a single data point on the volt-ampere characteristic. During the test, the load changes according to a predetermined sequence, with a flash occurring each time the load changes. A memory stores the measured data sequentially and summarizes them into a single volt-ampere characteristic curve. Another earlier device collected more than a dozen data sets during a single millisecond-long pulse flash and then combined them into a single curve. This required a very precise data acquisition system, and combining more than a dozen data sets to create a single volt-ampere characteristic curve was still relatively crude.

The advantages of the two pulsed test devices described above over steady-state testers are already quite obvious. First, power consumption is significantly reduced. Second, the temperature of the test piece is minimally affected by light during the test. However, challenges remain. First, measuring power consumption per square meter of composite panels still requires several kilowatts, making the equipment bulky and expensive. The long-arc pulsed xenon lamps used are relatively expensive, and the complex optical pulse formation circuitry, data accumulation, and processing systems make it difficult to reduce the price. Furthermore, the spectral characteristics of long-arc pulsed xenon lamps are not optimal, and the deviation from the solar spectrum is still large, thus reducing test accuracy.

As early as 1970, literature had theoretically pointed out the basic principle [M.S.Imamura, P.Brandtzaeg and J.L.Miller, "Solar cell dark I-V characteristics and their applications", Energy 70 Proceedings (The Fifth Intersociety Energy Conversion Engineering Conference), Vol. 1, P.10/38-45], that is, based on the dark characteristics of the solar cell and the voltage drop across the series resistor, its volt-ampere characteristics under illumination can be predicted. This solution further develops and improves the above principle, solves various specific technical problems, and becomes a technical solution that can be directly used to design solar cell testing equipment.

The same reference above derives the formula: _RS = _VD - _VL / _ISC , where _VL represents the solar cell's open-circuit voltage (VOC ₎ under illumination. _VD corresponds to the voltage at the top of the solar cell when the dark current equals the short-circuit current (ISC ₎ as measured by the dark characteristic. This _VD value can be found in the dark characteristic. From the calculated series resistance _RS and the dark characteristic, the solar cell's volt-ampere characteristic under illumination can be determined.

The present invention aims to overcome the shortcomings of existing pulsed test devices by making them portable, suitable for both indoor and outdoor testing. This invention eliminates the expensive long-arc pulsed xenon lamp and its complex associated circuitry, significantly reducing the cost of the test device and making it more widely available. It uses a photographic flash or similar short-pulse lamp as the test light source. The spectral characteristics of these short-pulse lamps closely resemble those of sunlight, eliminating the need for filters.

The principle of this scheme is as follows: The difference between a solar cell's volt-ampere characteristics under illumination and its dark characteristics is entirely due to the voltage drop across the internal series resistor _RS . By measuring the series resistor RS and the dark characteristics, the volt-ampere characteristics under illumination can be obtained. The dark characteristics can be easily measured using any conventional method, so the key lies in determining the series resistor RS.

This approach uses a photographic flash or similar short-pulse light source as the test light source. These light sources are inexpensive, have simple starting circuitry, are compact, and have spectral characteristics very similar to sunlight. However, the peak portion of the light pulse emitted by these short-pulse lights lasts only tens of microseconds or less, lacking a flat top. Therefore, directly measuring the full volt-ampere characteristics of a solar cell using a single light pulse is difficult. This approach uses only the peak value of the emitted light pulse to measure the solar cell's short-circuit current, I _SC , and open-circuit voltage, V _OC . The series resistance, R _S , is indirectly determined using the formula: R _S = V _D - V _L / I _SC , which is also the same as: R _S = V _D - V _OC / I _SC , where V _D can be found in the dark characteristic.

In this solution, the entire test process and data can be completed using a single-board microcomputer.

The following describes the specific steps of this solution with reference to the accompanying drawings:

Figure 1 is a block diagram for measuring the dark characteristics of solar cells. An automatic scanning power supply (1) is used as the test power source and is connected to the solar cell (2) under test via a small-resistance sampling resistor (3). The voltage Vd and current Id are taken from the solar cell (2) and stored in a microcomputer (6) via A/D converters (4) and (5), respectively.

Figure 2 is a block diagram for measuring the open-circuit voltage and short-circuit current of a solar cell. Measurements are made using the peak value of the light pulse emitted by a short-pulse lamp (7). When the automatically scanned electronic load (8) rapidly scans from open circuit to short circuit (or vice versa), the open-circuit voltage V _OC and short-circuit current I _SC are taken out by two sample-and-hold devices (9) and (10), respectively, and then input into a microcomputer (6) via A/D converters (11) and (12). If the scanning speed of the electronic load (8) is fast enough, only one flash of the short-pulse lamp (7) is required. If the scanning speed is slow, two consecutive flashes can be used to measure the open-circuit voltage V _OC and short-circuit current I _SC , respectively.

According to the above two steps, the internal series resistance R _S can be measured. Because the entire dark characteristic of the solar cell [2] has been measured in FIG1, and the open circuit voltage V _OC and short circuit current I _SC of the solar cell [2] have been measured in FIG2, and have been input into the microcomputer [6], a program can be set to allow the microcomputer [6] to automatically find the corresponding voltage V _D when the dark current value is equal to the short circuit current I _SC on the dark characteristic, and calculate according to the formula: R _S = V _D - V _OC / I _SC to calculate R _S and store it for future use.

Figure 3 shows how to convert the solar cell's dark characteristic [13] into its volt-ampere characteristic [15] under illumination. First, invert the dark characteristic and shift it upward so that its intercept on the current axis equals I _SC . This means replacing each point (Vd, Id) on the dark characteristic [13] with (Vd, I _SC - Id). This can be accomplished using a simple calculation program, resulting in the curve [14].

For the same current value, the voltage difference between the voltage on the volt-ampere characteristic under illumination [15] and the voltage on the curve [14] is I _SC R _S. Therefore, a calculation program can be set up to replace each point (Vd, I _SC -Id) on this curve [14] with (Vd-I _SC R _S , I _SC -Id) to obtain the volt-ampere characteristic under illumination [15].

It is not difficult to understand that the volt-ampere characteristic under illumination [15] can also be converted by the following method: set up a program to replace each point (Vd, Id) on the dark characteristic [13] with (Vd-I _SC R _S , Id) to obtain the inverted curve of the solar cell volt-ampere characteristic under illumination [15], and then replace each point (Vd-I _SC R _S , Id) on this inverted curve with (Vd-I _SC R _S , I _SC -Id) to also obtain the volt-ampere characteristic under illumination [15].

FIG4 is a block diagram of the current value near the operating point of the solar cell 〔2〕volt-ampere characteristic under illumination. To ensure test accuracy, the solar cell 〔2〕 is connected in parallel to an adjustable voltage-stabilized power supply 〔16〕 through a small-value sampling resistor 〔3〕. The adjustable voltage-stabilized power supply 〔16〕 is adjusted to the required voltage value near the operating point of the solar cell 〔2〕 (for example, a silicon single crystal solar cell is usually selected to be 410 millivolts). After the solar cell 〔2〕 is irradiated by a short pulse light 〔7〕, the current signal at that point is obtained from the sampling resistor 〔3〕 and sent to the microcomputer 〔6〕. The microcomputer 〔6〕 compares the current signal actually measured at that point with the current value corresponding to the same point on the volt-ampere characteristic 〔15〕 under illumination converted in the above steps according to the set program, and determines whether the error is within the specified index. If it exceeds, it immediately issues a command to retest, thereby ensuring test accuracy and increasing the reliability of the test device.

The advantages of this solution are that it uses a photographic flash or similar short-pulse lamp instead of an expensive long-arc pulse xenon lamp, eliminating the need for complex light pulse formation circuitry, data accumulation, and processing systems. This simplifies the device and reduces costs. Furthermore, the spectral characteristics of this short-pulse lamp closely resemble those of sunlight, improving test accuracy compared to long-arc pulse xenon lamps. During the entire test process, only a single or two to three short flash pulses, each lasting only tens of microseconds, are required. This reduces the power consumption of the entire test device to less than 100 watts, and the temperature of the solar cells being tested is completely unaffected. Compared to existing pulsed solar cell test devices, this device can reduce costs to less than one-tenth of their current cost. Furthermore, its compact size and light weight make it portable for field testing, increasing the testable solar cell panel area from the current maximum of several square meters to tens of square meters or even larger.

When implementing this solution, the short pulse lamp (7) is most conveniently and cheaply designed to be a photographic flashlight. The microcomputer (6) can be a single-board microcomputer such as the Z80, equipped with A/D and D/A converters and a microprinter. The electronic load (8) is preferably a microcomputer-controlled automatic scanning electronic load, preferably one that uses linear current scanning. The automatic scanning power supply (1) for measuring dark characteristics can be integrated with this automatic scanning electronic load (8) to form a single electronic circuit.

Claims (5)

1, a kind of test equipment of solar cells technical scheme, measure the dark characteristic [13] and the resistance in series RS value of solar cell [2] earlier, determine the volt-ampere characteristic [15] of solar cell under illumination [2] in view of the above, and then obtain various unit for electrical property parameters, feature of the present invention is to adopt photography multitime flash lamp or similar short-pulse light [7] as testing light source, the open-circuit voltage VOC and the short-circuit current ISC that only utilize the peak value of the light pulse of sending to measure solar cell [2] come indirect determination resistance in series RS value, and whole test process and data processing can be finished with monoboard microcomputer [6].

2, by the described test equipment of solar cells technical scheme of claim 1, it is characterized in that with an autoscan power supply (1) as the power supply of measuring dark characteristic (13), record solar cell (2) dark characteristic of volt-ampere characteristic (13) when not being subjected to illumination, and with each data-storing in microcomputer (6).

3,, it is characterized in that adopting the peak value of the light pulse that photography multitime flash lamp or similar short-pulse light (7) send to measure the open-circuit voltage V of solar cell (2) by claim 1 or 2 described test equipment of solar cells technical schemes _OCWith short-circuit current I _SC, the electronic load (8) that changes when autoscan scans short circuit by open circuit rapidly or when opposite, open-circuit voltage V _OCWith short-circuit current I _SCTaken out by two sampling holders (9) and (10) respectively, respectively through A/D converter (11) and (12) input microcomputer (6), the dark characteristic (13) that makes microcomputer (6) find out solar cell (2) goes up current value and equals short-circuit current I again _SCThe time terminal voltage value V _D, according to formula R _S=V _D-V _OC/ I _SCCarry out computing, obtain resistance in series R _SValue, and store stand-by.

4, by the described test equipment of solar cells technical scheme of claim 3, it is characterized in that being provided with microcomputer (6) calculation procedure, dark characteristic (13) is gone up every bit, and (Vd, Id) value replaces to (Vd, I _SC-Id) be worth, draw the inversion curve (14) of dark characteristic (13), and then again this inverted dark characteristic (14) is gone up every bit (Vd, I _SC-Id) value replaces to (Vd-I _SCR _S, I _SC-Id) value, promptly change the volt-ampere characteristic (15) of solar cell under the illumination (2) of asking, but also setting program (Vd, Id) value replaces to (Vd-I with every bit on the dark characteristic (13) _SCR _S, Id) be worth, draw the inversion curve of the volt-ampere characteristic (15) of solar cell under the illumination (2) of asking, and then again this is inverted every bit (Vd-I on curve _SCR _S, Id) value replaces to (Vd-I _SCR _S, I _SC-Id) value, the volt-ampere characteristic (15) under also convertible the illumination of asking.

5, by the described test equipment of solar cells technical scheme of claim 4, it is characterized in that in order to guarantee measuring accuracy, with solar cell (2) mutually and connect through a little resistance sample resistance (3) and an adjustable stabilized voltage supply (16), adjustable stabilized voltage supply (16) is transferred near required voltage value solar cell (2) working point, after solar cell (2) is subjected to short-pulse light (7) irradiation, from sample resistance (3), promptly obtain this current signal, send into microcomputer (6), microcomputer (6) by set order with this point survey current signal with change under the illumination volt-ampere characteristic (15) of solar cell (2) go up and compare corresponding to the current value of same point, as exceed, then send the instruction of resurveying once immediately.

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