All Electrical Drive Train for Marine Energy Converters (EDRIVE-MEC)

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Engineering

Abstract

EDRIVE-MEC: All Electric Drive Train for Marine Energy Converters

Conversion of energy from wave into electricity is ideally performed by a PTO and power conditioning system that can convert motion in multiple directions, react large forces or torques whilst operating at low velocity, variable voltage and frequency, with high reliability, availability and efficiency over a wide range of loads. All aspects of this demanding specification contribute directly to the Life Time Cost of Energy and hence economic feasibility of devices. At present no single PTO technology that has been demonstrated is able to meet this specification for wave energy. The two main options for the PTO used in a wave device: hydraulics and direct drive. Wave device developers have focussed on using hydraulics as the PTO, whether it be high pressure oil or water (Pelamis, Aquamarine). In discussions with our industrial partners we learnt that the only reason for using hydraulics was due its availability off the shelf, but all partners were concerned about the limitations including, low efficiency at part load; ability to control over a wide range of frequencies; and displacement leading to potential end-stop problems.

The alternative to hydraulics is direct drive, in which the mechanical interface is eliminated, but now the generator has to operate at low velocity and high force. Direct drive systems have been proven through lab tests at Durham and Edinburgh, and through sea trials by Uppsala in Sweden, Archimedes Wave Swing and Oregon State University. In each of these cases a permanent magnet synchronous machine has been used and the generator has been of a linear planar or tubular topology. Energy can only be taken out of the device from motion in one direction, principally heave, whereas devices surge and pitch as well as heave. The use of linear generators in their current form has constrained the functionality of direct drive power take off systems, as it has not allowed energy to be converted from more than one motion. No consideration has been given to speed enhancing techniques, such as magnetic gear boxes, as developed at Sheffield for rotary machines, or the use of springs, either internally produced through control, or external physical springs, such as air springs. Speed enhancing allows a more optimised machine design, resulting in a reduction in physical size and an increase in efficiency. Previous work in direct drive power take off has proved the concept will work, but solutions are not fully optimised, designed for reliability or matched to the characteristics of the wave device. As with the generator, developers have proved the concept of connecting direct drive systems to the grid, but making use of conventional power converter approaches. However, it is well known that there is a reliability issue with power converters in the wind industry, and in the tidal sector developers use an onshore power converter for easy access. The main cause of faults within the power converter is the continuous thermal cycling due to the variable nature of wind and wave. There is therefore an opportunity to investigate alternative power converter solutions, such as multi-level systems, where the stress on the power devices are now shared across a number of devices.

The main aim of the project has been formulated in discussions with our industrial partners: develop an integrated electrical power take off system with non-mechanical speed enhancement, integrated and reliable flexible power electronics, providing adaptive control over a range of operating regimes, taking into account nominal and extreme load conditions. E-DRIVE proposes to fulfil this aim through the development of novel integrated low speed generators with speed enhancement and power converter topologies with associated control to replace hydraulic systems. In doing so we will mirror developments in all/more electric systems in automotive and aerospace.

Planned Impact

The UK has one of the best marine renewable resources in the world. According to the Energy Technologies Institute (ETI) wave could generate up to 14% of UK electricity demand. In the last 5-10 years in the region of £700m of private and public money has been invested in marine renewables, wave and tidal. The Carbon Trust estimate that UK companies could take a 22% of the global marine market by 2050, worth £26b and leading to 20,000 jobs. The UK research councils have invested £24m in the establishment of the Supergen Marine Hub, associated grand challenge projects, doctoral training centres and the establishment of the unique FloWave Ocean Energy Research Centre at University of Edinburgh. It is clear that these investments have had significant impact on UK in terms of society, capacity building, economy, scientific development, international development and inward investment.. The component in the wave device that has received the least in terms of R&D funding is the electrical power take off (PTO), which converts the capture mechanical energy to electricity, as it is believed that the PTO is an "off-the-shelf" component that is used in the offshore oil and gas industry. However, many of the problems in the wave sector have been on the PTO, which mirrors the experience in the offshore wind sector. In its marine technology roadmap, the ETI consider the electrical power take off to be of a high priority for industry.
The main impact of EDRIVE is to demonstrate a new concept and produce new design tools specifically orientated to electrical power take off in wave energy converters. In doing so additional impact will be delivered as follows:
1. Industrial Engagement - WP7 in EDRIVE is focussed on engaging with our named partners (Carnegie (AUS/UK), Albatern (UK), Columbia Power Technologies (US), Tecnalia (Spain) and Turbo Power Systems (UK)) as well as engaging with additional wave device developers and the electrical power supply chain, in particular the eleccal machines & power electronics industry. To facilitate this engagement EDRIVE has established an Industrial Advisory Board, which will meet annually.
2. Investment and Wealth Creation - Wave energy has suffered major setbacks in the past 12 months with the closure of Pelamis and the scaling down of Aquamarine, thus investor confidence is low. EDRIVE will present at investor focussed conferences to demonstrate that the proposed research is contributing to the de-risking of wave technology. Investigators will participate in trade missions organised by UK and Scottish Government agencies to attract large international companies to the UK.
3. Scientific Advances - this represents the main academic impact, which will be achieved through dissemination at national and international conferences in electrical machines, power electronics and marine renewables, and in high impact international peer reviewed journals. EDRIVE will also report to relevant research hubs funded by EPSRC, namely UK Centre for Marine Energy (UKCMER) and the Centre for Underpinning Power Electronics widening access to the outcomes from the project. At international level we are working with TU Delft in the Netherlands and the University of Chile in Santiago.
4. Skills and People Pipeline - it is acknowledged that there is a skills gap in electrical machines and power electronics in the UK. EDRIVE's contribution to impact in this area will be through education activities such as Headstart to stimulate 6th formers, inclusion of material in undergraduate teaching, workshops for PhD students and postdocs, and finally tutorial sessions at conferences.
5. Policy - The Policy and Innovation Group at Edinburgh will inform national and international government policy through technology road-mapping, dissemination through the IEA Ocean Energy Group, the European Energy Research Alliance and the EU Ocean Energy Association, all of which Edinburgh is heavily involved in.

Publications

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Description We have received additional funding from the Marine Energy Alliance to work with Mocean Energy to develop direct drive and pseudo direct drive solutions. The project makes use of findings on magnetic gear research undertaken within E-DRIVDE.
First Year Of Impact 2019
Sector Energy
Impact Types Economic

 
Description PTO Stage 3
Amount £2,500,000 (GBP)
Organisation Wave Energy Scotland 
Sector Private
Country United Kingdom
Start 05/2017 
End 04/2019
 
Description Optimised C-GEN Direct Drive Generator for Mocean Energy. 
Organisation Mocean Energy
Country United Kingdom 
Sector Private 
PI Contribution Edinburgh is funded by the Marine Energy Alliance to work with Mocean on the development of direct drive and pseudo direct drive power take off for Mocean's wave energy device. Ben MCGILTON, formerly employed on E-DRIVE, is the researcher working on the project, and is using his PhD research that contributed to E-DRIVE.
Collaborator Contribution Mocean is providing details of their wave energy device, Blue Horizon, for the project. Regular engineering meetings are held between Mocean and Edinburgh.
Impact None yet
Start Year 2019
 
Description Power Conversion and Control of Wave Energy Converters in All Electrical PTO Systems 
Organisation University of Chile
Department Museum of Contemporary Art
Country Chile 
Sector Academic/University 
PI Contribution A member of the research team - Steve McDonald from Newcastle - spent a week in November 2016 at the Universidad de Chile with Prof Roberto Cardenas discussing the partnership and planned exchange of students in June-August 2017. One student will visit Newcastle and the other will visit Edinburgh. Maurcio Espinoza visited Newcastle for 3 months working on control of power converters, specifically the power converters being developed within E-DRIVE. He worked alongside Dr. McDonald, who was developing the power converters.
Collaborator Contribution Maurcio Espinoza (PhD student at Universidad de Chile) visited Newcastle for 3 months in 2018 working on control of power converters, specifically the power converters being developed within E-DRIVE. He also spent a week at Edinburgh learning about the generator and magnetic gear work being developed by the Edinburgh team. He is now an academic at University of Costa Rica. The Chilean partners will send two PhD students to the UK during June-Aug 2017, one working on power converter modelling at Newcastle University and the other will work on control of wave devices at University of Edinburgh.
Impact A journal paper has been published including the contribution from Mauricio Espinoza. McDonald SP, Baker NJ, Espinoza M, Pickert V. Power-take-off topology comparison for a wave energy converter. The Journal of Engineering 2019, 2019(18), 5012-5017.
Start Year 2017
 
Description The development of the power train for wave energy converters 
Organisation RMIT University
Country Australia 
Sector Academic/University 
PI Contribution Luke McNabb from RMIT University came to Newcastle for 3 months to work on control aspects of wave energy converters. Newcastle provided test rig facilities in the lab, and with Edinburgh additional testing was conducted at FloWave. As a result of Luke's work a conference paper has been accepted.
Collaborator Contribution Luke McNabb from RMIT University in Australia worked on control aspects of wave energy converters providing support to the Newcastle team, Baker and McDonald, in the development of the VHM linear test rig. Luke developed control systems, which were tested in the lab at Newcastle, and then on a scale wave device at FloWave at University of Edinburgh. The student exchange was funded by Australian Research Council Discovery Project DP170101039.
Impact The following paper will be presented at the IET PEMD Conference in Nottingham in April 2020. Development and testing of a small scale wave energy converter and fully controlled linear electric generator, N.J. Baker, L. McNabb, S McDonald, A. Almoraya, to be presented at 10th International Conference on Power Electronics, Machines and Drives (PEMD 2020). 2020, Nottingham, UK: IET
Start Year 2019
 
Title Edinburgh Wave Systems Simulation (EWSS) 
Description The EWST (Edinburgh Wave Systems Toolbox) is a suite of tools for the simulation of wave energy devices. EWST has the ability to model devices that are comprised of rigid bodies, power-take-off systems, and mooring systems. Simulations are performed in the time-domain by solving the governing WEC equations of motion in 6 degrees-of-freedom. EWST is derived from WEC-Sim, an open-source wave energy converter simulation tool developed in Matlab/Simulink using the multi-body dynamics solver Simscape Multibody. The EWST is also developed in Matlab, but drops the requirement for Simulink or Simscape Multibody. It also aims to be compatible with Octave, an alternative system able to process much of the standard Matlab code base. The hydrodynamic data format for both is identical, so hydrodynamic data can be easily ported between systems. EWST replaces the mutlibody modelling parts of the code with MBDyn, an advanced multiboy dynamics simulator. An advanced Matlab code based MBDyn preprocessor is available to allow the creation of MBDyn model input files directly from Matlab. Detailed documentation of the preprocesing tool may be found in it's own dedicated manual. Purpose With the existance of Wec-Sim the need for EWST may nt be obvious. EWST addresses several main perceived issues with Wec-Sim. 1. Maintainability: Wec-Sim being heavily based in Simulink does not lend itself to maintenance using standard software version control systems (e.g. Git, Mercurial). Simulink files cannot be easily compared for changes using these systems. 2. Debugability: Debugging a purely code based system is easier than one based in Simulink, as the ability to step through the code and navigate the different levels of the system is more advanced. purely code-based 3. Interface design: The developers of EWST have a different interface design philosophy which is more conventional than the WEC-Sim method. The EWST interface is more oriented toward automation and batch processing than the original WEC-Sim interface. This is mainly to facilitate randomised simulation and optimisation algorithms. 4. Modifiability: Being purely code based, and with all code in one location (rather than spread throughout Simulink models) 5. Cost: WEC-Sim requires many commercial platforms to be operated, EWST can be run entirely on free software (although the performance on Matlab will be superior). The EWST developers recognise that not everyone will agree with the points above or that they justify the creation of a separate system, but it was these needs which drove it's creation. An aim of the project will continue to be to maintain compatibility as much as possible between the two systems Developers and Contributers The Edinburgh Wave Systems Toolbox has been created by The Institute for Energy Systems at The University of Edinburgh as part of the EPSRC funded project "All Electrical Drive Train for Marine Energy Converters (EDRIVE-MEC)", grant No. EP/N021452/1. The main contributor is Dr. Richard Crozier. 
Type Of Technology Software 
Year Produced 2018 
Open Source License? Yes  
Impact Edinburgh Wave Systems Simulation software is being used by a Wave Energy Scotland Project - Project Neptune, led by University of Edinburgh, in order to develop design case studies for direct drive generator power take off for two industrial partners. 
 
Company Name Power Enabled Solutions 
Description The focus of Power Enabled Solutions is to develop control systems for renewable energy converters. It also undertakes consultancy on electrical machine design and wave and tidal energy systems. Dr. Richard Crozier was the researcher on EDRIVE, before estblishing Power Enabled Solutions with another researcher from University of Edinburgh/ 
Year Established 2018 
Impact Funded through iCURE, and Innovate UK. Dr. Richard Crozier developed the opensource Edinburgh Wave Systems Simulation Toolbox, available at https://sourceforge.net/projects/rnfoundry/.