Supercapacitor sizing based on comparative study of PV power smoothing methods

Power volatility of grid-tied photovoltaic (PV) sources can be responsible for various power quality issues in utility grids with high renewable sources penetration. Problems such as voltage flickering or frequency deviations can become more severe for isolated grids or islanded microgrids. Various solutions have been proposed to address these issues, mainly based on smoothing the PV output power by adding a storage device. In case of utilizing a hybrid PV/storage DC/AC converter, any abrupt changes in the power output of the PV due to cloud passing are absorbed by controlling the charge and discharge of the storage system. Therefore a storage system based on supercapacitors with quick time response and increased power density is proposed. This paper compares two different “power smoothing” methodologies in a PV installation, considering a supercapacitor in the common DC-link. The first power smoothing method is based on the moving average algorithm, while the second on controlling the rate of change of the power injected to the grid. The main target focuses on providing comparative results for both control strategies, by implementing simulation tests with real irradiation measurements. A comparative study is also conducted for the sizing of the energy storage, based on the real irradiation profile created to remark the real energy needs of the installation and prevent over-sizing of the supercapacitor. The results show a significant difference in storage size, depending on the power smoothing method implemented, thus a careful consideration of the grid requirements is necessary.