Researchers from Pakistan's Ghulam Ishaq Khan Institute of Engineering Sciences and Technology have created an online algorithm to measure open-circuit voltage in PV systems that is claimed to be able to estimate voltage, current and temperature of a PV system without interrupting the power flow to load.
Described in the study Performance evaluation of online open-circuit voltage estimation method for photovoltaic system, published in SN Applied Sciences, the new technique is also said to provide higher accuracy than the two temperature sensor method, which is one of the most common temperature sensing techniques in PV modules. This consists of applying two sensors on a panel to measure its ambient temperature and the cells' temperature, respectively. “This method accurately estimates the open-circuit voltage in variable irradiance condition,” the scientists said. “However, this method does not perform well in variable temperature conditions.”
The proposed technique and the two temperature sensor method were both tested on a 245 W PV panel from Chinese manufacturer Yingli (Yingli YL245C-30b) under variable environmental conditions. Through the former, open-circuit voltage is calculated without isolating the module and the single diode model of the panel is used for the estimation. The panel is also interfaced with load through a boost converter and three sensors are used for the measurement of the voltage, current and temperature. “All the sensors are interfaced with micro-controller Arduino UNO which gives the short-circuit voltage value,” the academics specified.
The test showed that the overall average calculated error for the three-sensor online method is 0.087% and that it performed well under different conditions. “The average calculated error of the online and two temperature sensor method for the complete duration is 2.65% and 14.85%, respectively,” they stated. “Thus, it is verified from the practical results that the accuracy of the online method is significantly higher than the two temperature sensor method.”
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