Mitigation of Solar PV Intermittency Using Ramp-Rate Control of Energy Buffer Unit

The unpredictability of the solar irradiance fluctuations can result in both photovoltaic (PV) power output fluctuations and high ramp rates. This can lead to significant voltage fluctuations with high ramp rates at the point of common coupling. Traditionally, the energy buffer units (EBUs) are used to smooth out the power fluctuations using the moving average method or the PV power gradient control. However, these methods can only smooth out the power at the output of grid inverter without considering the local load. This paper proposes a power management strategy to address this issue with two main operation modes: first, the load-feeding mode to minimize the grid power consumption by maximizing the local load consumption from both the PV and the EBU; second, the grid-feeding mode to smooth out the PV output fluctuation and to control the ramp rate to a desired value when supplying the grid. Furthermore, the EBU can be fully charged during the off-peak period or at night by the grid to take advantage of the time-of-use electricity price. The proposed control strategy is first simulated using MATLAB/Simulink and then a laboratory prototype platform is built and tested to verify the feasibility and the effectiveness of the proposed power management strategy with ramp-rate control.