Model for photovoltaic cells in series under uneven lighting conditions

When the PV array encounter sun even illumination or partial occlusion conditions, the output characteristics between the different modules is no longer consistent. For a series circuit, the current flowing through is completely consistent. If putting the photovoltaic cells of the different characteristics in series, some battery is able to carry out full load power generation while some cannot achieve full power output. This is because the shaded cell is weak at power output. The maximum output current, also known as short-circuit current, limits the capability of the entire branch. This will lead to the emergence of the hot spot and thus damage the battery. Parallel diode photovoltaic cells are bale to solve the uneven illumination of the hot spots. When the current in the main circuit exceeds the short-circuit current in one of the cells, the parallel diode will bypass the cell. Although the bypass battery does not participate in output power, the whole branch is still able to output a higher power. Hence, it is still cost-effective overall. However, the multi-extreme phenomenon caused by applying the bypass diodes needs to be represent using piecewise functions. This paper presents a simple and practical engineering model of photovoltaic battery function. The piecewise functions are simplified and integrated into one single function. The accuracy of this model is validated by comparing the simulation curves and experimental data.