Analysis and control of mismatch power loss in photovoltaic arrays

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Abstract
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 cell degradation through localized heating of individual cells. Such problems can arise simply through the shading of a single cell. In this paper, which has a substantial tutorial content, three methods of reducing the effects of mismatch are investigated and compared; the use of integral bypass diodes (IBDs), series/paralleled circuit designs and reduced cell shunt resistance.Experiments were performed on arrays incorporating cells with IBDs and their tolerance to shading was tested and compared to arrays with other cell designs. the potential benefits and costs of using IBDs are then assessed and conclusions drawn about the relative effectiveness of this strategy. the circuit design strategy known as series/paralleling is described and analysed and its effect on minimizing mismatch power loss is evaluated. Also, an expression for the optimum cell shunt resistance in a general shaded array is derived and the technique of reducing cell shunt resistance to minimize mismatch effects is assessed.

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