Model Predictive Control of a Wave Energy Converter with Discrete Fluid Power Power Take-Off System

Hansen, Anca Daniela; Asmussen, Magnus Færing; Bech, Michael Møller

doi:10.3390/en11030635

Cited by 25 publications

(21 citation statements)

References 17 publications

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“…One branch of digital hydraulics considers multi-chamber cylinders. Here the conventional control valve is replaced by several on/off valves which may be supplied by multiple pressure lines (Hedegaard Hansen et al, 2017;Linjama et al, 2003;Hedegaard Hansen and Pedersen, 2016;Hedegaard Hansen et al, 2018). In Donkov et al (2017Donkov et al ( , 2018 a simulation study investigating actuation of a knuckle boom crane using the digital hydraulic technology was conducted.…”

Section: Introductionmentioning

confidence: 99%

A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock

Ketelsen¹,

Andersen²,

Ebbesen³

et al. 2020

MIC

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This paper presents a self-contained pump-controlled hydraulic linear drive including an innovative load holding sub-circuit. For safety critical applications such as crane manipulators, locking valves or load holding valves are enforced by legislation, but the load holding functionality may also be used actively to decrease the energy consumption for applications where the load is kept stationary for longer periods of time. The system proposed in this paper is based on a simple hydraulic architecture using two variablespeed electric motors each connected to a fixed-displacement pump. This architecture is well-known in academic literature, but in this paper a novel load holding sub-circuit has been included. To control this load holding functionality, the low chamber pressure needs to be controlled accurately, while still being able to control the motion of the cylinder piston as well. Due to strong cross-couplings between cylinder piston motion and chamber pressures this task is non-trivial. The control for opening the locking valves is indirect in the sense that it is controlled via the chamber pressures, which are actively controlled. The fundamental control strategy presented in this paper is based on transforming the highly coupled physical states to virtual states, significantly reducing cross-couplings. As a case study, a two link medium sized knuckle boom crane is selected as an application example. Simulation results confirm the applicability of the proposed system. Appropriate position tracking performance has been achieved for the considered motion trajectory, while the low chamber pressure is controlled in a satisfying manner. A smooth transition from motion operating mode to load holding mode is achieved, with the system not requiring any input energy to keep the load stationary when the hydraulic cylinder lock is engaged.

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Section: Introductionmentioning

confidence: 99%

A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock

Ketelsen¹,

Andersen²,

Ebbesen³

et al. 2020

MIC

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“…Apart from that, the combination of active valves operation, such as in a typical hydraulic PTO concept presented in Figure 6b, also can be used to control the hydraulic PTO force as investigated in [48,91,104]. For example, in [91], the multi-level control strategies have been invented for typical WEC with hydraulic PTO concept presented in Figure 6b.…”

Section: Hydraulic Cylinder With An Active Control Valve Mechanismmentioning

confidence: 99%

“…Furthermore, a similar concept of control strategies in [91] also has been implemented in a multi-chamber hydraulic actuator-based PTO system [104]. In this study, the WPEA based on the model predictive control (MPC) principle has been invented to maximise the wave energy production by cleverly manipulating the PTO force.…”

Section: Hydraulic Cylinder With An Active Control Valve Mechanismmentioning

confidence: 99%

Hydraulic Power Take-Off Concepts for Wave Energy Conversion System: A Review

et al. 2019

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Ocean wave energy is one of the most abundant energy sources in the world. There is a wide variety of wave energy conversion systems that have been designed and developed, resulting from the different ways of ocean wave energy absorption and also depending on the location characteristics. This paper reviews and analyses the concepts of hydraulic power take-off (PTO) system used in various types of wave energy conversion systems so that it can be a useful reference to researchers, engineers and inventors. This paper also reviews the control mechanisms of the hydraulic PTO system in order to optimise the energy harvested from the ocean waves. Finally, the benefits and challenges of the hydraulic PTO system are discussed in this paper.

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“…The discrete PTO system is based on the discrete displacement cylinder technology that features a multi-chamber cylinder connected to a number of constant pressure lines, see for example, Reference [19]. The feasibility of MPC based WPEA's for discrete PTO systems was established in Reference [20], where promising performance was reported. The current paper focuses on how prediction models may be simplified to allow models that are computationally light.…”

Section: Introductionmentioning

confidence: 99%

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

2019

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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.

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Model Predictive Control of a Wave Energy Converter with Discrete Fluid Power Power Take-Off System

Cited by 25 publications

References 17 publications

A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock

A Self-Contained Cylinder Drive with Indirectly Controlled Hydraulic Lock

Hydraulic Power Take-Off Concepts for Wave Energy Conversion System: A Review

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

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