Tidal currents are the result of oceanic flow caused by tides and are a source of renewable energy. The tides reverse direction every half cycle, with one cycle taking between a half day to a full day, depending on location. It is therefore possible to predict the power generated by a tidal current power generation system. Such systems are similar to wind power generation systems in their approach to producing power from a fluctuating input source. There has been particular interest in tidal current power generation systems operating at variable speeds, converting tidal current energy into electrical energy with high efficiency. Previously, we investigated the rated capacity of the generator and the gear ratio required to maximize the annual generated energy, given that the power generation system operates with constant rotor voltage control and maximum power point tracking control up to the annual maximum current speed. This shortens the time during which the generator operates at its rated capacity, thereby reducing the annual generated energy per unit capacity of the generator. In this study, we investigate the rated capacity of the generator and the gear ratio required to maximize the annual generated energy when the maximum current speed for power generation is set to less than the annual maximum.
