The Output Characteristic Predicting Of PV Array In Arbitrary Condition

Because of the special properties of the solar cell, if the research of the solar power systems adopts true photovoltaic array, will produce a series of questions such as the high cost of experiment , needing a large number of spacious field, strong dependence on insolation level and natural climate. If the solar cell output characteristics can be predicted at different insolation level and ambient temperature accurately, as well as the array that the cells are connected in parallel and series output characteristics can be predicted, thus the maximum power can be analysed. A large number of experiment cost may be saved.First of all, a fast, accurate method for extracting the solar cell (module) model parameters is put forward. Based on solar cell current model, the current equation is transformed from the complicated transcendental equation into the simple algebraic equation by differential coefficient to current equation and simplifing at short circuit, combining with the description at the maximum power point to set up a close algebraic equation group for solving the series resistance, the shunt resistance, the photo-generated current, the reverse saturation current density and the diode ideal factor, then educe analytic solutions of various model parameters. At last, using nonlinear fitting optimizes the analytic solutions. This method on the one hand improves the precision of extracting parameters , on the other hand greatly improves the stability.Next, predicting the solar cell (module) performance. The solar cell (module) manufacturers provide only an I-V curve under the standard test condition, but the solar cell (module) actually does not work at the standard testing condition. Thus, the prediction of the solar cell (module) output characteristics under various working conditions is very necessary. A method can accurately predict the module output characteristics under different working conditions which only needs a measured I-V curve under standard testing conditions is present in the third chapter. This method, firstly, extracts the solar module model parameters using an I-V curve under standard testing conditions. Secondly, together with the relationships of model parameters varying with illumination intensity and cell temperature, the prediction of solar module output characteristics under different work condition is made. Finally some significant phenomena of solar module characteristics impacting the maximum power is discussed. The results show that the photo-generated current and the diode ideal factor at the standard testing condition have greater influence on the module P-T and P-S characteristics. Some useful supplements are put forward on the principles of series and parallel. The photo-generated current of individual cell in series at the standard testing condition is equal besides the current of maximum power, the diode ideal factor of individual cell in parallel at the standard testing condition is equal besides the voltage of maximum power.When analysing the output characteristics of photovoltaic array, series connected module need study voltage separately and parallel connected module need study current separately. But the implicit I-V equation expression can not be used to study current and voltage separately, which make the analysis for characteristics of series and parallel connected module difficult. But the explicit expressions of current and voltage which based on the Lambert W function make analysing current and voltage separately possible. The relationships between the array parameters and the modules parameters respectively are showed for individual module parameters being identical and different, thus the output characteristics of array are predicted. For photovoltaic array with bypass diodes and block diodes, the output characteristics of array are accurately described by subsection function. Uneven illumination and temperature impacting the output characteristics of array is demonstrated.A simulation model for photovoltaic array simulator is developed under Matlab environment, based on solar cell five parameters model, together with the relationships of model parameters varying with illumination intensity and cell temperature ,and modern power electronic technology,The model fully simulates the main circuit structure of solar cell. The I-V characteristics of photovoltaic array without diode and with diode can be simulated at any corresponding insolation level, ambient temperature. The results have great theoretical significance for developing the simulation model that can completely simulate the output characteristics of array under different working conditions .