Physical and Mathematical Modeling of a Wave Energy Converter Equipped with a Negative Spring Mechanism for Phase Control

Abstract

A wave-energy converter has been studied through the combination of laboratory experiments and numerical simulations. The converter model is a semi-submerged axi-symmetric buoy with a circular cross section with a diameter of 26 cm at the water plane. The buoy is pitching about a fixed external axis oriented such that the buoy works primarily in heave. The laboratory model is equipped with a spring mechanism referred to as WaveSpring, which works to shift the resonance period and increase the response bandwidth of the system. A controlled electric actuator was connected and programmed to provide a velocity-proportional force for power extraction. The buoy mass was varied at two levels and the experimental setup was exposed to a selection of regular and irregular waves. The power take-off (PTO) damping was set as a function of sea state. A mathematical model for global motion response was developed based on linear hydrodynamic theory and rigid-body dynamics. Comparison of laboratory measurements and numerical simulation results shows that the dominant physical effects have been well captured by the mathematical model. Overall, the study gives an experimental verification that a negative spring mechanism mounted in parallel with the power take-off machinery of a wave energy converter may be used to increase the average converted power.

Hydraulic Experiments on a Small-Scale Wave Energy Converter with an Unconventional Dummy Pto

“…This is the case selected for the experiments, as described in Sub-Section 3.2. Another example is the pre-stressed piston applied to the Weptos in [21], who described the possible benefits of a negative stiffness mechanism in terms of combined wave-PTO interaction (later confirmed by [22]).…”

A Flower Pollination Method Based Global Maximum Power Point Tracking Strategy for Point-Absorbing Type Wave Energy Converters

“…The phase and amplitude control of heaving-buoy WEC constrained by amplitude are described in [15][16][17], where the phase control is applied to keep the velocity of the buoy in phase with the excitation force of waves, producing a result similar to locking. This method is effective for achieving the maximum power extraction of the point absorber.…”

“…The hill-climbing method cannot search the global maximum power point among multiple extreme points, due to its monotonous search Currently, various control methods of point-absorber type WEC for optimizing wave energy capture have been proposed, where the implementation complexity, the accuracy and the tracking speed of these techniques are different. These control techniques can be classified into four categories: (1) phase and amplitude control [15][16][17][18], (2) complex conjugate control [19][20][21], (3) model predictive control (MPC) [22][23][24], and (4) extremum-seeking control [25].…”

Data-Driven Control Techniques for Renewable Energy Conversion Systems: Wind Turbine and Hydroelectric Plants

“…The trend to reduce the use of fossil fuels, motivated by the need to meet greenhouse gas emission limits, has driven much interest in renewable energy resources, in order also to cover global energy requirements. Wind turbine systems, which now represent a mature technology, have had much more development with respect to other energy conversion systems, e.g., for biomass, solar, and hydropower [1]. In particular, hydroelectric plants present interesting energy conversion potentials, with commonalities and contrast with respect to wind turbine installations [2][3][4].…”