Control Strategies for Reconfigurable PV Modules

Abstract

PV systems in urban environments frequently get shaded by nearby objects, which greatly reduces their yield. A potential solution for such situations is the use of reconfigurable PV modules. They are a type of modules which can reconfigure themselves under varying illumination conditions to ensure optimum yield at all times. The individual PV cells of the module are grouped into reconfigurable units/ cell blocks which can be interconnected in various ways to form a variety of unique configurations. The modules have an inbuilt algorithm which is responsible for controlling the reconfiguration process. There are various kinds of reconfiguration algorithms found in literature, each working with varying input parameters and operating principles. One such algorithm is the short circuit current sensing (SCCS) algorithm developed by the PVMD research group at TU Delft. The algorithm is meant for series-parallel
connected reconfigurable modules and uses each cell block’s short circuit current as input. It is a synchronous reconfiguration algorithm, which means it runs at regular time intervals and not when there is actually a change in the module’s irradiance conditions. Therefore, the aim of this thesis was to develop a robust reconfiguration algorithm with a shade detection mechanism. Consequently, numerous versions of a reconfiguration algorithm with shade detection mechanism were defined and tested using a simulation framework for modelling reconfigurable PV modules. It was observed that the reconfiguration algorithm that performed the best in terms of yield, reconfiguration count and accuracy was the one referred to as the ”CC4AP+IR algorithm”. The algorithm uses the module’s and a single cell block’s operating current and voltage as inputs for shade detection. It was observed that the algorithm reconfigured a fraction of the time that the SCCS algorithm reconfigured and had a DC yield comparable to the SCCS algorithm. The new algorithm was also tested using real-life data to validate its performance. This experiment indicated that if the module were to be run using the new reconfiguration algorithm instead of the SCCS algorithm, it would have run only 6% of the time that the SCCS algorithm ran, but have a comparable DC yield. The significantly lower reconfiguration count is relevant because in practice, the PV modules are connected to power converters which will not be able to tolerate the high fluctuations in output owing to frequent reconfigurations.