MPP Tracking Losses of Module Level Power Electronics at Partial Module Shading

Power optimisers aim to reduce shading effects when operating a PV system and promise a massive increase in yield. In recent years, the real performance benefits of such Module Level Power Electronic (MLPE) components have been -tested in a few isolated trials. The results support the statement that PV systems with power optimisers deliver an increased yield compared to string inverter systems in certain cases with complex and pronounced shading situations. On the contrary, their effect may even be detrimental in low complexity scenarios for several reasons. This paper focuses on a specific topic, the analysis of losses associated with Maximum Power Point (MPP) tracking. The MPP adjustment is analyzed in an indoor test setup and the cases correspond to typical outdoor partial shading using a commercially available MLPE. It is shown that the adaptation to changing conditions works well with small changes in the associated MPP voltage, but fails with larger voltage jumps, such as those that occur with increased shading and activated bypass diodes. The observed effects are also verified in a real system. The preference for a higher voltage and lower current can be advantageous with regard to hot spots but reduces the overall yield.