Electrical Design for Ocean Wave and Tidal Energy Systems
Renewable energy is expected to play a major part in future energy supplies, both to reduce the impact on the world climate and also to make up for any shortfall in conventional energy sources. Ocean energy has the potential to make a significant contribution to future renewable energy supplies as identified in recent reports from the Intergovernmental Panel for Climate Change and the International Energy Agency. Ocean energy is an emerging industry sector and there are a number of promising developments under way. Significant commercial deployments in the gigawatt range are envisaged over the next 10 to 20 years in Europe, USA, Asia and South America.Electrical Design for Ocean Wave and Tidal Energy Systems gives an electrical engineer's perspective of this technology, addressing offshore wave and tidal power stations, grid integration and distribution. With contributions from a panel of leading international experts, this book is essential reading for electrical design engineers, researchers and students working in ocean energy development and renewable energy. Topics covered include generator selection and rating; electrical energy storage; grid integration; power quality; cabling, umbilicals and array layout; modelling and simulation techniques; control theory and realisation; power system issues; and economics of ocean energy electrical systems.
Inspec keywords: realisation theory; power generation economics; wave power plants; distribution networks; wave power generation; offshore installations; power supply quality; submarine cables; power cables; tidal power stations; power generation planning; power system simulation; energy storage; power grids
Other keywords: electrical energy storage; power generation economics; power distribution; umbilical cables; control realisation theory; power quality; ocean wave energy systems; power system modelling simulation; grid integration; offshore wave tidal power stations; tidal energy systems; underwater cable
Subjects: Tidal power stations and plants; Wave power; Submarine cable systems; Power system planning and layout; General and management topics; Control of electric power systems; Storage in electrical energy; Tidal and flow energy; Monographs, and collections; General electrical engineering topics; Power system management, operation and economics; Other energy storage; Power supply quality and harmonics
- Book DOI: 10.1049/PBRN017E
- Chapter DOI: 10.1049/PBRN017E
- ISBN: 9781849195614
- e-ISBN: 9781849195645
- Page count: 400
- Format: PDF
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Front Matter
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1 Introduction
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2 Electrical generators in ocean energy converters
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This chapter provides an outline of the issues confronting the designer of an ocean energy converter (OEC) when selecting or designing the electrical generator and its associated control system. It is clear that, especially for wave energy converters (WECs), this is a complex problem due to the high variance in device power take-off (PTO) type, and indeed the functionality of the generator itself within the power chain. Specification and design of the generator system in tidal energy converters (TECs) have been reviewed and shown to be highly dependent on the device, turbine and current characteristics. Both squirrel cage induction generators (SCIGs) and permanent magnet synchronous generators (PMSGs) are promising generator technologies for application in TECs, showing individual advantages and disadvantages. As important as the choice of the generator technology are the concepts to deal with the special requirements of TEC devices like marine environment, submerged operation and extended maintenance intervals. A consistent requirement in both WEC and TEC system generators is the need for variable speed control and operation. In this context, the power converter technology and controller algorithms related to this need have been introduced.
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3 Cabling umbilical and array layout
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This chapter discusses the case of dynamic cables and subsea connectors for which the design requirements and specifications posed by marine energy applications are distinctly different from the ones typically applied in the offshore industry. Bespoke solutions are needed in this case as the design of the connection is largely dependent on the device dynamics and the deployment location. This chapter reviews applicable standards and procedures for cable components and highlight the most important issues associated with marine energy projects.
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4 Grid integration: part I - power system interactions of wave energy generators
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This chapter presents an overview of the main issues associated with a wave energy generation system from a power system's standpoint. Issues specifically related to the time profile of power exported from a wave energy power plant are considered, and the impact of this fluctuating power on the power system performance is addressed. Some of these issues are covered in greater depth in future chapters. The need for reactive power compensation equipment, particularly in far offshore farms, is considered and addressed. The off-grid type of operation is also described. Most of the principles are illustrated with simplified models of wave energy generators (WEGs) with sinusoidal type outputs.
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5 Grid integration: part II - power quality issues
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The importance of complying with power quality requirements is essential as failing to meet them is a sufficient reason for any grid operator to deny grid connection applications. However, limits specified by these requirements may differ among different grid connection codes, rendering compliance with power quality requirements somewhat site-specific. This is expected to change due to the increasing level of harmonisation of grid codes.
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6 Grid integration: part III - case studies
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This chapter details four case studies addressing the grid integration of wave and tidal current energy. The first three studies focus on the power quality issues arising from the connection of a tidal device or of a wave farm on their local network. More specifically, the first study investigates the impact of the SeaGen tidal turbine connected at Strangford Lough, Northern Ireland. The two other studies focus on the grid impact of a medium-size wave farm on its local network. The last study addresses the challenges in terms of grid integration at a power system level and details the capacity value of wave energy in Ireland.
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7 Electrical energy storage systems
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This chapter examines electrical energy storage systems (ESSs) for wave energy converters (WECs). The motivations for including on-board energy storage are outlined in terms of power smoothing, low-voltage ride-through (LVRT) and ancillary services. Various wave energy converter technologies are explored as well as their inherent energy storage mechanisms. Electrical energy storage technologies, including batteries, capacitors, and supercapacitors, are then compared. Two case studies are described where electrical energy storage, namely supercapacitor energy storage, is applied to help smooth the output power from a WEC. The first case study examines power smoothing for a SEAREV WEC and the second case studies explores smoothing the output power from an offshore oscillating water column (OWC) WEC operated at variable speed.
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8 Control systems - design and implementation
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This chapter discusses the control systems for ocean, wind and wave energy. A general study on wind turbine control suggests that a variable-speed turbine, requiring torque and speed control, can absorb 2.3% more energy than a fixed-speed counterpart, where the speed is fixed by the electrical grid frequency. In the case of wave energy, the numbers are more dramatic. A study on latching control, which is a relatively simple implementation of the more ideal complex-conjugate control, suggests that energy capture can increase by as much as afactor of 2 with control in irregular waves and by up to a factor of 4 in regular waves.
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9 Modelling and simulation techniques
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Tidal turbine dynamic performance analysis requires the use of computational models representing the nonlinear differential-algebraic equations of the various system components such as tidal resource, turbine, generator, converter, control system and grid connection. However, the main difficulty is to include a variety of sub-models with different timescales for hydrodynamic loads. The user is therefore concerned with selecting the appropriate models for the problem at hand and determining the data to represent the specific turbine equipment.
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10 Economics of ocean energy electrical systems
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This chapter aims to present the expected costs for ocean energy electrical systems and some of the major challenges faced by ocean energy in this area. The chapter also looks at techno-economic optimisation of array layouts and goes on to explore some potential strategies to reduce the cost of ocean energy electrical systems. The focus is mainly on wave energy electrical systems.
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Back Matter
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