Hydraulics & Maritime Research Centre hmrc.ucc.ie Charles Parsons Energy Research NUIM Ocean...

Hydraulics & MaritimeResearch Centre

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Charles Parsons Energy ResearchNUIM Ocean Energy Seminar, October 21st 2010

National Ocean Test Facility

Generator Requirements and Functionality for Ocean Energy

ConvertersDr. Dara O’Sullivan

Hydraulics & Maritime Research Centre, UCC

21st Oct 2010

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Overview

Evolution of generator technology Common requirements of OE generators Device specific requirements of OE

generators Generator functionality within OE devices

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Traditional Generators

Synchronous Fixed speed Fault current – 3-4 pu Field regulated reactive power

Turbine

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Technology Migration

Asynchronous

Two-speed

Variable Speed

Variable SpeedGearless

Driven by Wind Turbine Development

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Technology Drivers

Energy Capture – MPPT Mechanical Robustness – drive-train torque

loads Grid Connect Codes Reliability

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What about OE Generators?

Are the issues the same as wind? What are the differences?

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Generator Requirements

Common Device Specific

Environmental

Grid Connect

Speed Range

Torque Rating

Custom or OTS

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Operation and Maintenance

High cost – minimise requirement!Tidal – Expensive to perform at bestWave – weather windows

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Brushed Generators

Typical brush life – 3-8k hrs Twice yearly maintenance/replacement –

corresponds with wind industry best practice Brushes are considerably more inaccessible

in many OE devices Brush film formation disrupted in oscillatory

current flows – significantly enhanced wear

Brushed generators may be unsuitable for OE devices

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Corrosion

Saline air exposure Not air conditioned generator enclosures PMGs sensitive Special coatings available e.g. VACCOAT

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Mechanical Design

Significant heave and pitch accelerations in many devices e.g. OWC:Pitch: 7deg/s2

Pitch: 4 m/s2

2x bearing rating due to gyroscopic loads

Robustness important

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Grid Connection

Voltage Limits Voltage Distortion Flicker Reactive Power Control Requirements Active Power Control Requirements Fault Ride-Through

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Voltage Distortion

Local Voltage

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Generator Grid Connect OptionsFully variable speedReactive power controlControlled fault ride-through

‘Fixed’ speedNo reactive power controlNo fault ride-through

Fixed speedReactive power control Controlled fault ride-through

Limited variable speedLimited reactive power controlControlled fault ride-through

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Device Specific Requirements

Oscillating Water Column Hydraulic Point Absorber Overtopping Device with Hydro PTO Direct Drive Point Absorber Tidal Turbine Tidal Oscillating Hydrofoil

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Oscillating Water Column

Air turbine with limited range of efficient operation

Variable speed OTS design High peak-to-average

torque ratio

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Hydraulic Point Absorber Generator design

strongly linked to hydraulic circuit design

Fixed speed possible OTS possible Hydraulics can absorb

torque pulsationsWavebob Prototype

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Overtopper Conventional hydro

turbines High pole or gearbox

coupled Rating equals maximum

mean power Fixed speed possible Wave Dragon prototype

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Direct Drive Point Absorber

Direct drive linear or rotary generator Custom design Must have power electronics conversion Low speed and high torque High part load efficiency very important

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Tidal Devices

Tidal turbinesMarine equivalent of wind turbinesHigher gear ratios

Oscillating hydrofoilsSimilar to hydraulic point absorbers

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Functionality

Determines how the generator sits within the power conversion chain1. Power conversion

2. Prime mover efficiency optimisation

3. Power smoothing

4. Damping control

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SummaryOEC Prime Mover Speed

Range Generator Peak Torque

RangeGenerator Type

OWC 600-1500 rpm 2-4 pu; reduces with added inertia

VS SCIG/SG/PMG

PA - hydraulic

1000-3000 rpm Close to 1 pu with high accumulator storage, up to 4 pu as storage reduces

FS SG/SCIG-SVC for high storage designs

VS SG/PMG/SCIG for low storage designs

Overtop 100-250 rpm Close to 1 pu GBC: FS SG/SCIG-SVC or VS PMG/SCIG

Low speed VS PMG

PA - direct

0-3m/s 0-400 rpm

2-5 pu; reduces with added inertia

Linear: PMG (custom) Rotary: GBC VS SG/PMG

Tidal turbine

0-10 rpm Close to 1 pu GBC, FS SG/SCIG-SVC or VS SG/PMG/SCIG

Tidal hydrofoil

1000-3000 rpm Close to 1 pu FS SG/SCIG-SVC for high storage designs or VS SG/PMG/SCIG for low storage designs

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THANK YOU

QUESTIONS?

Hydraulics & Maritime Research Centre hmrc.ucc.ie Charles Parsons Energy Research NUIM Ocean...

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