Hardware-in-the-Loop Validation of Model Predictive Control of a Discrete Fluid Power Power Take-Off System for Wave Energy Converters

Abstract

Model predictive control based wave power extraction algorithms have been developed and found promising for wave energy converters. Although mostly proven by simulation studies, model predictive control based algorithms have shown to outperform classical wave power extraction algorithms such as linear damping and reactive control. Prediction models and objective functions have, however, often been simplified a lot by for example, excluding power take-off system losses. Furthermore, discrete fluid power forces systems has never been validated experimentally in published research. In this paper a model predictive control based wave power extraction algorithm is designed for a discrete fluid power power take-off system. The loss models included in the objective function are based on physical models of the losses associated with discrete force shifts and throttling. The developed wave power extraction algorithm directly includes the quantized force output and the losses models of the discrete fluid power system. The experimental validation of the wave power extraction algorithm developed in the paper shown an increase of 14.6% in yearly harvested energy when compared to a reactive control algorithm.

Electro-Hydraulic Variable-Speed Drive Networks—Idea, Perspectives, and Energy Saving Potentials

“…The schematic of this VDN-PP is already depicted in Figure 9B, and when including the cross-port leakage and drain flows, its pressure dynamics may be described by Equations ( 11)- (13). Here,…”

“…The flow decoupling scheme for the VDN-PP can be derived for the individual axes as they are hydraulically separated. The load and sum pressure dynamics may be found from Equations ( 10)- (13) as Equations ( 35)- (38), when neglecting cross port leakage and drain flows:…”

“…The field of digital hydraulics has mainly evolved via two paths being digital flow control units and digital displacement units. In both cases, the switching valves and their control play a crucial role for system performance and efficiency [1][2][3][4][5]; however, the energy saving perspectives of digital hydraulics are indeed present and potential application areas broad [6][7][8][9][10][11][12][13][14][15].…”

Research Status and Prospects of Control Strategies for High Speed On/Off Valves

“…Digital hydraulic technology is considered to be a potential solution to replace traditional hydraulic servo control technology in the "Industry 4.0" era [10]. Digital hydraulic technology is now used in a wide variety of fields, such as aircraft braking systems [11], aircraft actuators [12], construction machinery [13,14], conveyors [15], and wave energy recovery systems [16]. Digital valves mainly consist of incremental digital valves and high speed on/off valves (HSV), of which the former have been abandoned by academia and industry due to its low-frequency and tendency to become out-of-step.…”

On Real-Time Hybrid Testing of Ocean Wave Energy Conversion Systems: An Experimental Study

“…These techniques are also gaining popularity in the WEC development sector [24], and hardware-in-the-loop (HIL) experiments can be a very powerful tool; for example, controller hardware-in-the-loop (CHIL) and power hardware-in-the-loop (PHIL) experimental testing for a renewable energy system integration [25]. The majority of the literature related to HIL focuses on experimental setups consisting of small scale rotatory motor-generator testbeds to simulate ocean hydrodynamics and wave energy converter dynamics [26]- [30], or hardware test rigs tailored for some particular type of WEC device, such as hydraulic PTO [31] and raft-type WEC [32], inertial mechanism-based WEC [33] and dielectric elastomer generators [34]. A limited amount of work is directed towards HIL testing of Linear PTO mechanisms, such as in [35], [36]; however, the scope of the work is limited to specific WEC in their facilities.…”