The laboratory tester of solar cells with dynamic reconfigutration of measuring system

Abstract

An express meter of photovoltaic solar cells based on the programmable system on a chip PSoC5 and a personal computer is proposed. This tester is best suited for research on experimental samples of solar cells with non-standard dimensions and parameters, but can also be used as a standard tester for standard samples to control their characteristics with high precision. For the implementation a minimum of discrete elements — a PSoC5 chip, a transistor and
a couple of resistors and diodes are required. And such devices as voltage supplies and a computer are available in each laboratory. The standard test conditions (irradiance 1 kW per sq.meter; spectral distribution AM 1.5; sample temperature 25^oC) are conditions that obtainable in a laboratory by using a xenon single flash tube or by an incandescent lamp with filter to reduce the red part of spectra. Despite of the simplicity of the implementation the tester performs measurements of the basic parameters of solar cells (open-circuit voltage, short-circuit current, internal serial resistance and shunt resistance, maximum power, voltage and current at maximum power, efficiency, fill factor, short circuit current density) with high precision and charting current-voltage characteristic of solar cell during less than a second. All the parameters and the current-voltage characteristic are automatically saved to a file and can be examined later. Advantages of the tester are a low cost and highly flexible implementation of the measuring system that allows you to explore experimental samples of solar cells with different characteristics. This was implemented through the use of dynamic reconfiguration of system on a chip that adapts to the conditions of measurement. Depending on the photoelectric current, the algorithm, written in the memory of the programmable system on a chip, selects the appropriate configuration of the measuring system and adjusts the bit resolution (up to 20 bit) and type of the analog-to-digital converter, and gain of the built-in amplifier to provide a minimum time of measurement and maximum of accuracy at given conditions. This allows researchers to reduce the time for investigation of objects with unknown characteristics at a given measurement accuracy. In addition, a sufficient number of additional hardware resources of the programmable system on a chip (digital blocks for logic, timers, counters, analog blocks for operational amplifiers, a programmable gain amplifier, comparators, mixer sample and hold circuit, etc.) with the possibility of their easy configuration into the electronic circuit in the graphic mode of the PSoC Creator allows to researchers easily and quickly to fill up / adjust the electrical scheme to their needs without  the need to change the circuit board of the device. The presence on the PSoC of the ARM Cortex-M3 32-bit CPU and the 24-bit fixed-point digital filter processor allows the researcher to supplement the measurement circuitry with digital signal processing, which is especially relevant for small-scale research samples with weak signals in the presence of noises.

Ref. 10, fig. 7.