Horizontal-axis tidal current turbines have considerable potential to harvest renewable energy from ocean tides. The pitch control system is a critical part of variable-pitch tidal turbines. Existing control strategies for tidal turbines mainly rely on flow measurement devices to obtain tidal velocities, which are costly and subject to many limitations in practical applications, making them unsuitable for small off-grid tidal turbines. In this paper, we propose a pitch control strategy for a 120 kW horizontal-axis tidal current turbine based on the output power of the generator. The torque of the turbine was calculated based on the blade element momentum theory, and a dynamic model of the tidal turbine was established. The dynamic characteristics of the turbine and generator were studied under various flow rates and pitch angles. On the basis of the characteristic analysis, the generating efficiency of the unit was improved under a low flow rate, and the output power was limited to a rated value under high-current velocity by regulating the pitch angle. Furthermore, a novel protection and start up strategy is proposed to protect the unit and make full use of the tidal energy when the tidal current velocity exceeds the limit value. We performed simulations, the obtained results of which demonstrate the effectiveness and advantages of the designed control strategies.

Under the action of waves, a small unmanned surface vehicle (USV) will experience continuous oscillation, significantly impacting its photovoltaic power generation system. This paper proposes a USV photovoltaic power generation simulation model, and the efficiency of photovoltaic MPPT control under wave action is studied. A simulation model for solar irradiance on solar panels of USV under wave action is established based on CFD and solar irradiation models. The dynamic changes in irradiance of USV solar panels under typical wave conditions are analyzed. The MPPT efficiency of USV photovoltaic power generation devices under continuously changing irradiance conditions is studied on this basis. The simulation research results indicate that waves and solar altitude angles significantly impact the instantaneous irradiation energy of USV photovoltaic devices. However, the impact of waves on the average irradiance is relatively tiny. The sustained oscillation of irradiance poses certain requirements for the Maximum Power Point Tracking (MPPT) control frequency of USV photovoltaic systems; a disturbance control frequency of no less than 50 Hz is proposed.