An Adaptive Ramp-Rate Control for Photovoltaic System to Mitigate Output Fluctuation

With high penetration level of grid-connected photovoltaic (PV) system, the stability of power grid is easily affected by the variable irradiation which furthers the power fluctuations with high ramp-rate. Hence, in order to extent the proportion of solar energy in power grid, a method for controlling ramp-rate is necessary to be installed in PV system. Normally, energy storage system (ESS) is employed without a direct control and controllable ramp-rate in prior-arts. Meanwhile, the state of charge (SoC) of ESS could also influence the fluctuation mitigation performance. In this paper, an adaptive ramp-rate control is proposed with integrated ESS for fluctuation mitigation. This control blends a direct ramp-rate control to reduce the fluctuation caused by PV side irradiation change to a desired level and a SoC control with variable ramp-rate to improve the performance in unexceptional SoC. The proposed control is verified by the simulations based on a typical PV micro-grid with ESS.