Power smoothing by controlling stored energy in capacitor of photovoltaic power system

Installation of the photovoltaic power system on the roof of houses is increasing rapidly. The photovoltaic power system has two typical problems, one is large power output change depending on climate change, and the other is over voltage in distribution line due to reverse power flow. These problems will be remarkable subjects for large amount of installation of photovoltaic power system in near future. This paper discussed countermeasures for these problems. We propose an output power smoothing method that a dc capacitor is assumed and stored energy is controlled to make the output smooth, an idea for determining the capacity of the capacitor based on measured data is explained. We also propose a flexible control for a photovoltaic power system with active power and reactive power controls against conventional one that has constant unity power factor, because reactive power is able to contribute over voltage suppression in distribution line. Proposed controllers are applied to a photovoltaic power system for a single phase ac output with three wires, and performance is confirmed by ATPDraw simulation.