RECONFIGURATION STRATEGY FOR OPTIMIZATION OF SOLAR PHOTOVOLTAIC ARRAY UNDER NON-UNIFORM ILLUMINATION CONDITIONS

摘要

Performance of a solar photovoltaic (SPV) array is affected by variations in temperature, solar insolation and array configuration. At times, the SPV arrays are susceptible to non-uniform illumination due to shading caused by passing cloud, towers, trees etc. The effect of partial shading is critical; it can cause problems such as irregular P-V characteristics (multiple peaks) which makes power optimization difficult by the conventional power extraction techniques and results in significant loss of power. In most SPV systems, a DC-DC converter is connected at the SPV output to compensate for the drop in the PV output voltage. Under shaded conditions, a high gain DC-DC converter is needed to boost the low SPV voltage, which leads to additional power loss. Under such conditions, an appropriate reconfiguration scheme may prove to be beneficial as it ensures a certain minimum voltage for the next stage, obviating the need for high voltage gain, thereby reducing the power losses in the DC-DC converter. Under non-uniform illumination conditions, the P-V characteristics may exhibit multiple peaks. In the absence of reconfiguration, the conventional power optimization technique will get trapped at the local maxima and result in loss of power. While reconfiguration shows advantage in power as well as makes the P-V characteristics less irregular making the convergence to the maximum power point easier. This paper proposes a reconfiguration strategy which ensures a certain minimum deviation from the operating voltage with improvement in power. A reconfigurable 4×4 solar PV cell array is designed. The experimental results for a 4×4 cell array demonstrating the reconfiguration strategy showing improvement in power has been included. And simulation results of reconfiguration of flexible PV modules under non-uniform conditions are also provided.