Modeling Output Characteristics Of Photovoltaic System Under Arbitrary Irradiance And Temperature

The determination of solar cell model is important in the design, evaluation anddiagnosis of Photovoltaic (PV) systems. Therefore, a model of the PV system is neededin determining its output characteristics under arbitrary irradiance and temperature.Based on the equivalent photovoltaic circuit model with single exponential term, theeffect of the model parameters on the I-V characteristic curves, especially theshort-circuit current, open-circuit voltage and the max power point, was analyzed. Aniterative method is introduced to extract the solar cell parameters of equivalent circuit,using electrical parameters provided by the manufacturer and a semi-empirical parameterto estimate the shunt resistance. An explicit expression of I and V was obtained by usingthe Lambert W function, based on which the method for calculating model parameters ofthe photovoltaic array was given. Knowing the configuration method of a PV array,namely the parallel number Np and the series number Ns, the five model parameters canbe quickly and simply calculated by using data from the module manufacturer.The influence of the irradiance and cell temperature on the model parameters istaken into account which makes the model adaptable to irradiance and temperatureconditions other than STC (Standard Testing Conditions). A simple empirical efficiencymodel of grid-connected PV inverter was also obtained by using polynomial curve fittingmethod. Therefore, based on the above models, the output characteristics of a PV systemunder arbitrary conditions can be calculated. The comparison between the experimentaldata and simulation results shows good reliability and accuracy of the proposed model.The error is less than1%at STC, and less than5%at other conditions.A simulation model is built in the Matlab Simulink environment. The model ishelpful in studying the characteristics of the MPPT strategy and can be used to estimatethe daily output of the PV array. From the comparison between measured and modeledpower output, the model shows its effectiveness in predicting the theoretical maximumoutput power of an PV array, and is proved helpful in the diagnosis of PV generationsystem.