Research On Explicit Modeling Methods For Single-diode Model Of Solar Cells

In order to realize optimal design and optimal operation of the PV power generation system, a simulation model is demanded. PV array, composed of a group of photovoltaic cells by series and/or parallel combination. Therefore, the modeling of photovoltaic cells is an essential research topic. In general, electrical equivalent circuit is used to describe the model of a solar cell. There are two kinds of the popular electrical equivalent circuits for a solar cell. One is an electrical equivalent circuit with one diode, named single-diode model. The other is an electrical equivalent circuit with two parallel diodes, named two-diode model. However, the mathematical expressions of the two models are implicit and nonlinear equations about current and voltage. In order to obtain the current value corresponding to a voltage value, numerical analysis algorithms have to be used to solve the implicit equation. However, there will be no solution under improper initial guess. Therefore, it is necessary for engineering designers to present an accurate, fast explicit analytical expressions for I -Vcharacteristic of solar cells.In the paper, three explicit modeling methods are presented, and the explicit analytical expressions are obtained. Firstly, Lagrange interpolation polynomial and five key points which is available from the Sandia National Laboratories are used to approximate I -Vcharacteristic of solar cells, an explicit analytical expression can be obtained. I -Vcharacteristic of solar cells is widely used to estimate the maximum power point. However, the method based on Lagrange interpolation polynomial cannot estimate the maximum power point. Next, Spline interpolation polynomial and three key points from the Sandia National Laboratories are used to approximate I -Vcharacteristic of solar cells. The three key points do not contain the maximum power point. Based on this method, an explicit analytical model of solar cells is obtained to describeI -Vcharacteristic and estimate the maximum power point. Lastly, Chebyshev Polynomials method is proposed to express the exponential function of I -Vcharacteristic equation and the two modified five-parameter models by using Chebyshev Polynomials are obtained. According to the electrical parameters provided by manufacture, the cell parameter, i.e. Photo current, diode reverse saturation current, shunt resistance, series resistance and ideality factor parameter are obtained and then the value of voltage can be directly obtained according to the given value of current. Furthermore, the key parameters,such as short-circuit current, open-circuit voltage, the current and the voltage at the maximum power can be also obtained based on the parameters provided by manufacture. To validate the accuracy of the models proposed in the paper, different photovoltaic modules with the different technology types are tested at different irradiance and temperature conditions, and a comparison between the proposed models and the other models are made.