Noriyuki Uchiyama

Harmonic current reduction control for grid-connected PV generation systems

Integration of renewable energy sources (RES) with significant capacity, including photovoltaic (PV) generation systems, into the grid is expected within ten years. Such RESs bring to the grid not only their benefits but also some technical problems, as increase of harmonic currents. Compliance with the technical requirements for harmonic current is necessary for successful increase of RES capacity. A scheme to reduce harmonic current for grid-connected PV generation systems was developed. This control scheme effectively reduced harmonic current in the grid current of the PV generation system caused by voltage distortions at the grid. Experiments using a prototype of the power conditioning system (PCS) showed its validity. 400-kW PCSs with the control scheme have been installed and have been in service since the end of 2009.

Supply and demand control of distributed generators in a microgrid

Distributed generators (DGs) that use renewable energy sources have an unstable output and this can negatively affect existing electric power systems. To reduce this impact, we developed an energy control system for controlling the output from individual DGs that were installed in a microgrid. Controlling the DGspsila outputs enabled the power fluctuation at the point where the microgrid was connected to the existing power grid to be reduced. The microgrid was installed and operated in two separate locations for a total of 672 days. The actual DGs were photovoltaic power generation (PV) systems, fuel cells, and a NaS battery. We demonstrated that 99% of the power imbalance between the supply and demand over 10-, 15-, and 30-minute periods was within a range of plusmn3% under normal operating conditions when using our power control system. Furthermore, we demonstrated that, by using our power control system, the power flow fluctuation of the PV systems output at the grid connection point was smoothed.