Progress is being made around the world on introducing renewable energy sources such as solar and wind power as a response to the problem of global warming and to reduce dependence on oil and other fossil fuels. However, the outputs of these renewable energy sources are not constant and can be unstable because they depend on the terrain, level of sunlight, and other environmental factors at the installation site. There are concerns that if significant numbers of large-scale photovoltaic power generation systems are incorporated into the electricity grid in the future, they will cause voltage and frequency fluctuations that interfere with the operation of the grid. As a result, technologies are needed to deal with these problems. When developing a high-capacity power conditioning system for use with large-scale photovoltaic power generation systems, Hitachi incorporated two new functions that did not previously exist. These were a function for reducing grid voltage fluctuation and an FRT function for coping with transient voltage drops. A harmonic suppression function that reduces the flow of harmonic currents was also incorporated (see Fig. 1). These functions contribute to future-oriented large-scale photovoltaic power generation systems that can help maintain the stability of the power grid.