Intermittent wave energy generation system with hydraulic energy storage and pressure control for stable power output

In this paper, we introduced an intermittent wave energy generator (IWEG) system with hydraulic power take-off (PTO) including accumulator storage parts. To convert unsteady wave energy into intermittent but stable electrical output power, theoretical models, including wave energy capture, hydraulic energy storage, and torque balance between hydraulic motor and electrical generator, have been developed. Then, the integrated IWEG simulator was constructed and tested at the Ningbo Institute of Technology. Through a series of experimental tests, the relationship between operating flow rates and pressure drops across the hydraulic motor was established. Furthermore, on the basis of the pressure drop signal, we proposed a feedback control method on the basis of the pressure drop database as the feedback control signal to eliminate the disturbance of periodic peak pressure impulse through the regulation of the opening ratio of a proportional flow valve and achieved the effective and stable electric power output, albeit intermittently. Compared with the previous complex control theories and algorithms, this method can keep the power output more stable over a wide range of operating conditions. Furthermore, experimental tests indicate that the IWEG system, with hydraulic PTO, including hydraulic accumulator and proportional flow control valve, is simple, reliable, and easy to control. Most importantly, the real-time power output is stable, and power quality and generation efficiency are significantly improved

Offshore wind system in the way of Energy 4.0: ride through fault aided by fractional PI control and VRFB

This chapter presents a simulation of a study to improve the ability of an offshore wind system to recover from a fault due to a rectifier converter malfunction. The system comprises: a semi-submersible platform; a variable-speed wind turbine; a PMSG; a 5LC-MPC; a fractional PI controller using the Carlson approximation. Recovery is improved by shielding the DC link of the converter during the fault using as further equipment a redox vanadium flow battery, aiding the system operation as desired in the scope of Energy 4.0. Contributions are given for: (i) the fault influence on the behavior of voltages and currents in the capacitor bank of the DC link; (ii) the drivetrain modeling of the floating platform by a three-mass modeling; (iii) the vanadium flow battery integration in the system