Study On Optimal Control Of Photovoltaic Array Power Generation Efficiency Under Partial Shading Conditions

In recent years,with the increasing demand for natural resources,the extraction of traditional fossil fuels has increased rapidly,which has inevitably led to a global energy shortage and severe environmental pollution caused by the combustion of fossil fuels,and these problems are forcing human society to seek new solutions.It is therefore an urgent issue nowadays to discover and develop an efficient clean energy resource.Solar energy is being increasingly valued by academics and specialists in various fields as a clean and efficient alternative source of energy that is readily available on the planet.A major contributing factor to the rapid development of the photovoltaic（PV）industry is the free and inexhaustible nature of the raw material known as sunlight.Therefore,PV technology as a form of energy conversion has been regarded as a hot topic in the current evolution of the energy field.To maximize the conversion of light energy collected by PV modules into electrical energy,it is necessary to implement a power conditioning system（PCS）within the PV system which enables the PV modules to operate at their optimum state in real time.However,due to the time-varying external environment,unpredictable string mismatches occur frequently in large-scale PV systems,which makes the PCS of conventional PV systems unable to detect and precisely locate the optimal operating state of the overall system,thus resulting in severe power losses and even system hot spot failures to fire situations.Under partial shading conditions（PSCs）caused by clouds,neighboring buildings and animal excrement such as birds,the power-voltage characteristic curve will become complicated and have multiple peaks for each parallel string of PV modules within the array,which will undoubtedly increase the difficulties for the PCS to determine the maximum power point（MPPT）of the array.However,determining the global MPPT of a PV array and extracting the full power of each string of PV modules within the array is a critical factor for improving the efficiency of PV power systems.Hence,we propose a system called Active PV array（APV）system along with its control strategy to address these issues.It ensures that the system is able to operate at its MPPT in real time even when the irradiance is changing dramatically due to unpredictable environmental variations.The research object of this paper is a PV system under partial shading conditions,and the main research is as follows.（1）In this paper,the power-voltage characteristics of PV arrays are simulated and analyzed using PSIM software,and the power generation of conventional PV system and APV system at large PV plant scale are being compared.The simulation results demonstrate that the APV system has a power enhancement effect on the output power from the ideal natural conditions level,which provides feasibility support for further experiments.（2）To verify the feasibility of the Active PV array system in practical production situations,an experimental platform was set up and an operational test experiment of the APV system under partial shading conditions was performed,as well as a long-term power enhancement comparison experiment.First of all,the strain of the APV system was tested under artificially altered external environmental conditions,and the experimental results fully demonstrate the system’s ability to adapt to various harsh and unexpected conditions.Secondly,a long time power enhancement comparison experiment was executed for two small PV arrays composed of the identical kind of models under the very same natural conditions,and the power output at the end of the two PV systems in the comparison group was observed under the same shaded experimental environment,where the experimental results confirmed the high efficiency and reliability of the APV system.（3）This study initiatively proposes an upgrade solution to enhance the power generation efficiency of PV arrays by adding DC-DC converters in PV arrays,supplemented by corresponding control strategies,which can address the retrofitting work of conventional PV power generation systems currently in service.In addition,this solution provides a solution to the mismatch problem between different types of PV modules faced by the current PV arrays when being extended.In summary,this study provides a high-efficiency solution for traditional PV system facing PSCs,where the output power decreases significantly,and where the PV modules in the array affected by shading may suffer from hot spot problems.At the same time,the solution is also economical and convenient for the upgrade project of old PV plants.