ANALYSIS AND CONTROL OF MISMATCH POWER LOSS IN PHOTOVOLTAIC ARRAYS

Connecting photovoltaic cells to form an array can cause problems when the characteristics of the cells are not matched. This problem, known as mismatch, can reduce the power output of the array and lead to cel l degradation through localized heating of individual cells. Such prob lems can arise simply through the shading of a single cell. rn this pa per, which has a substantial tutorial content, three methods of reduci ng the effects of mismatch are investigated and compared; the use of i ntegral bypass diodes (IBDs), series/paralleled circuit designs and re duced cell shunt resistance. Experiments were performed on arrays inco rporating cells with IBDs and their tolerance to shading was tested an d compared to arrays with other cell designs. The potential benefits a nd costs of using IBDs are then assessed and conclusions drawn about t he relative effectiveness of this strategy. The circuit design strateg y known as series/paralleling is described and analysed and its effect on minimizing mismatch power loss is evaluated, Also, an expression f or the optimum cell shunt resistance in a general shaded array is deri ved and the technique of reducing cell shunt resistance to minimize mi smatch effects is assessed.