Very small-scale hydropower plants are environmentally friendly and renewable
resource-based innovative solutions. The interest in pico-hydro systems (up to 5 kW) has
increased significantly from the first stand-alone applications, at remote sites, to the distributed
generation, with the injection of generated energy into the grid. Recently, there have been
advances in the grid connection of these systems using off-the-shelf components, namely
photovoltaic inverters. Therefore, pico-hydro systems have gained an enormous potential in
distributed generation, particularly in the context of microgrids. However, in situations of
over-power, or whenever the generator is under no load, e.g. when the grid fails, there is
a need for effective over-voltage protection, as in small wind turbines. This paper proposes
two over-voltage protection circuits, designed to ensure the integration of pico-hydro turbines
connected to the grid using conventional photovoltaic microinverters and string inverters, for
power ranges of 300 W and some kW, respectively. Extensive tests were performed on an
emulation platform and a workbench using these two different over-voltage protection circuits.
One is designed to connect the generators of water wheels to the grid and the other to
connect 1,500 W generators of water turbines. The experimental results demonstrated the
performance of the proposed over-voltage protection circuits in four different situations. Both
avoid irreversible damages of generators, photovoltaic microinverters and string inverters in
the context of the above-described grid connection approach.
