Coordinated Control of Arrays of Wave Energy Devices—Benefits Over Independent Control

Abstract

It is well known that control systems, which can modulate the power takeoff force of a wave energy device, have the capability of extending the effective device bandwidth and thereby improve energy capture. For an array of wave energy devices, there is the additional complication that each device is subject to radiated waves from other devices, which are a function of the device motion and, hence, an indirect function of each of the device controllers. This gives the possibility of enhancing the energy harvesting properties of the wave farm as a whole, by giving each controller information about the motion of other devices and employing a global performance function which allows coordinated control for the overall benefit of the farm. This paper examines the possibilities of using such coordinated control and makes conclusions on the types of devices, and types of arrays, that might benefit from such coordinated control. In addition, the overall benefit of a global array control strategy, compared to independent control of each device, is assessed against the added complexity of a coordinated control strategy. Index Terms-Control, power optimization, power takeoff, wave energy arrays. Giorgio Bacelli received the Laurea Magistrale in electronic engineering from Università Politecnica delle Marche, in 2006. He worked on his thesis as a Socrates student at the Electronic Engineering

Control, forecasting and optimisation for wave energy conversion

“…There are many new promising areas where control can make further contributions in wave energy applications, including cooperative control of arrays of wave energy devices (Bacelli et al, 2013;Bacelli and Ringwood, 2013a;Li and Belmont, 2013). For example, for the sample array layouts of Fig.15, Fig.16 shows the ratio (E i /E g ) of energy captured by an array of heaving cylinders (radius=4m, draught=10m and resonance period=7.1s) with independent device control (E i ) and global coordinated control (E g ) in a sea with peak period T p = 12s (λ = 225m).…”

“…Empirical validations of the Morison equation have proven its validity and methods have been proposed to evaluate the coefficient C d for certain specific shapes (Bhinder et al, 2012;Yuan and Huang, 2010). In addition, a linear approximation to (13) may be derived, using an energy matching technique (Bacelli et al, 2013), if desired.…”

A resistance emulation approach to optimize the wave energy harvesting for a direct drive point absorber

“…11, the P ratio -γ curves in the simulations have a similar shape, in the sense that the captured power increases with the damping coefficient up to a maximum point, and it then starts to decrease. It can be noted that the P ratio -γ curves are quite different in P ratio , because regular waves carry more energy per meter of wavefront, as shown in (16) and (17). However, for both regular and irregular waves, the optimal damping coefficients are almost coincident.…”

“…Based on these predictions, different methods to optimize the captured power can be found in [13]- [15]. Furthermore, it is important to ensure an efficient control of a single WEC so that the strategy can be extended to the control of a wave farm, as in [16].…”

Coordinated Control of Wave Energy Converters Subject to Motion Constraints

“…It should be noted that, in the above articles, no constraints are considered in those frequency models. More recently [28,29], a time domain model was developed to calculate the optimal PTO damping for individual WECs at each time instant. This model can handle the constraints on motions and PTO force.…”