Research On Pv Array Structure Optimization Based On Shadow Recognition Algorithm

Partial shading causes some PV modules in the array whose operating points deviate from their own MPPs,which leads to the mismatch power loss.According to the actual shadow distribution,the dynamic structure optimization method can reduce the mismatch power loss by changing the electrical connection of the PV array in real time.However,the current structure optimization methods detect the shadow by many sensing elements,and calculate output characteristics by considering the PV module as the minimum unit in simulation,which results in the reconfigured array is not the optimal one.Therefore,it has significant theory and practice values to design a simple and effective structure optimization method for the irregularly shaded PV array.In this dissertation,the optimal reconfiguration method for the PV array is proposed based on digital image process technology and mathematical modeling.The main contributions of the dissertation are listed as follows:(1)Considering the features of the PV array images,a shadow recognition algorithm is proposed for the detection of the PV shadow.The algorithm is divided into the cell recognition part and the shadow recognition part.To reduce the disturbance of the silver-white grid lines on the module,the grid line smoothing method is adopted.Besides,an improved local threshold segmentation is employed for each cell region of the module to avoid the influence of the color aberration among the PV modules and increase the efficiency of the shadow recognition.(2)The irradiance approximation error for the output characteristics on partially shaded module and array are discussed in detail using specific cases and data.Based on the discussion,a simplified simulation method for PV array's output characteristics is proposed specific to each PV cell.According to the actual shadow on the PV array,the modules are divided into three kinds: unshaded,totally shaded and partially shaded.By formulating different simulation schemes for each kind of module,the output characteristic of the PV array can be acquired accurately and quickly.(3)A new PV array reconfiguration method based on shaded cells' number is proposed by analyzing the determinant factors on MPP's output power.This method detect the shadow distribution accurately by adopting shadow recognition algorithm.After sorting the PV modules according to the number of shaded cells,two candidate configurations are constructed.Using the simplified simulation method,the optimal configuration for maximizing the output power is calculated,and thus the electrical connection of the PV array is changed correspondingly.Multiple simulation results indicate that the proposed method can increase the output power of the PV array and is applicable to the array under different shadow distributions.