A Review of Wave-to-Wire Models for Wave Energy Converters

Abstract

Control of wave energy converters (WECs) has been very often limited to hydrodynamic control to absorb the maximum energy possible from ocean waves. This generally ignores or significantly simplifies the performance of real power take-off (PTO) systems. However, including all the required dynamics and constraints in the control problem may considerably vary the control strategy and the power output. Therefore, this paper considers the incorporation into the model of all the conversion stages from ocean waves to the electricity network, referred to as wave-to-wire (W2W) models, and identifies the necessary components and their dynamics and constraints, including grid constraints. In addition, the paper identifies different control inputs for the different components of the PTO system and how these inputs are articulated to the dynamics of the system. Examples of pneumatic, hydraulic, mechanical or magnetic transmission systems driving a rotary electrical generator, and linear electric generators are provided.

Validating a Wave-to-Wire Model for a Wave Energy Converter—Part II: The Electrical System

“…Such W2W models should include balanced parsimonious models for each stage (including nonlinear dynamics if required and considering the constraints and losses of each component), meaning that the level of detail included in the sub-models for the different stages of the W2W model is balanced. The most important aspects to be considered when modelling W2W models are reviewed in [11] for several different PTO systems (pneumatic [12], hydraulic [13], or a mechanical transmission system [14] coupled to a rotational generator, or a direct drive system with a linear generator [15]), which have been suggested in the literature for different WECs.…”

“…In the case of oscillating-body WECs, hydrodynamic power is given by the multiplication between the device velocity (ẋ), induced by the excitation force (F exc ), and the PTO force (F PTO ) and can be maximised subject to design limitations by means of different control strategies [6], including advance Full conversion chain of a wave energy converter with hydraulic power take-off (PTO); adapted from [11].…”

Advances and Challenges in Wave Energy Park Optimization—A Review

“…The dynamics of WECs differ fundamentally from those of traditional offshore structures, mainly due to the small scale of the WEC structures, the existence of a PTO, and the aim to absorb energy from the waves, which often requires large-amplitude motion at resonance with the waves. Many different PTO systems and methods of modeling them exist in the literature (see Folley et al, 2013;Day et al, 2015;Forehand et al, 2015;Penalba and Ringwood, 2016). For instance, the PTO can be a hydraulic system driving a rotating generator, a hydro-or air-turbine, or a linear direct-driven generator.…”

Validating a Wave-to-Wire Model for a Wave Energy Converter—Part I: The Hydraulic Transmission System

“…Figure 1 shows the different stages of that chain that need to be incorporated in the W2W models, including the control inputs for each stage (α, β and γ). The most important aspects of all conversion stages in W2W models are reviewed in [1] for different power take-off (PTO) configurations: pneumatic [2], hydraulic [3] or mechanical transmission systems [4] coupled to a rotational generator, or even direct drive systems with linear generators [5]. The W2W model validated in the present paper is designed as a combination of inter-connected sub-models, where each sub-model can take a different time-step by implementing multirate time-integration schemes [12,13].…”