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WP 3

Power-Take-Off Systems

03-09-2010

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Work Package 3

Work package partners:

Department of Energy Technology of the University of Aarlborg (AAU-E)

Fraunhofer Institute for Windenergy and Energy System Technology (IWES)

Research areas:

Electrical rotating and linear generators

Energy storage systems

Simulation of PTO-systems

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Overview

• WEC concepts and impact on the PTO-systems

• Generator systems

• Energy storage systems

• Simulation of PTO-Systems

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Oscillating Water Column

Oscillating Bodies Overtopper

Energy conversion step 1

Air-chamber Oscillating body Water-ramp/water-reservoir

Energy conversion step 2

Fast rotating air-turbine

Hydraulic PTO Slow rotatingturbine

Generator system Rotating generator Linear or rotating generator

Rotating generator

Integrated energy storage system

Turbine, generator Hydraulic-Tank,generator

Water-reservoir,generator, turbine

WEC Concepts

Oscillating Water Column Oscillating Bodies Overtopper(picture: Ocean Energy) (picture: PELAMIS) (picture: WaveDragon)

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WEC concept:

Overtopper: generator system for low turbine speed

Oscillating body: linear generator designed for high force

Structure of generator system depends on WEC concept

Grid connection:

Smooth power delivered to the grid

General requirements:

Efficiency

Life time

Overload capacity

Scalability

=> Costs

Criteria for Generator System Design

€

(picture: WaveDragon)

(picture: Transpower)

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ASG gear box

Three conversion steps:

1 – adaption to turbine speed

2 – conversion to electrical power

3 – grid connection Generator system components

Speed increaser

- Mechanical- Hydrodynamical- Hydrostatical

Generator - Induction generator- Doubly fed induction

generator- Synchronous generator

Frequency converter

- Intermediate voltage circuit

- Current-source - Direct converter

Components for Rotating Generator Systems

Generator system design:

Specification/choice of components

according to the criteria

Typical generator system

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Rework criteria considering partload

System 1: three-stage gearbox + doubly fed induction generator (DFIG)

System 2: high-pole permanent magnetic

synchronous generator (PM)

Variation of Generator System

(picture: WaveDragon)

Adaption to low turbine speed:

box gear

ASG System 1:

System 2:

System comparison:

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Fluctuating power input Energy Storage System Smooth grid power

Wave characteristic

Period time: ..5..10 seconds

Power frequency = 2 * wave frequency

Requirements

High cycle lifetime

Short charge / discharge time

Single device <-> farm solution

Integrated storage systems

Inertia of rotating components

Hydraulic system

Water-reservoir

Impact on PTO

Derating of generator system

Damping of PTO-system

Degree of freedom for plant control system

Energy Storage Systems

(picture: Enercon) (picture: Transpower)

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Storage System Wh/kg W/KG Life time (cycles)

Efficiency(%)

Cost(US$/kWH)

Battery 35-130 150-350 700-1000 75-95 150-2000

Ultracapacitor 5 2000 500.000 93-98 25.000

Flywheel 40 3000 5000 90 20.000

Characteristics of Storage Systems

(picture: DETA) (picture: WIMA) (picture: Enercon)Battery Ultracapacitor Flywheel

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Design Process Tasks

• Definition of criteria for WEC

• Identification of system/components

• Benchmark of systems according to criteria

• Verification of choosen system/components -> simulation

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Sub model components

Requirements:

Multiphysic system simulation

Large component model libraries

Interface to overall model

High performance

Use cases:

Reliability investigations

Yield calculations

Operation control verification

Compoment dimensioning, etc

Modelling of PTO-System

(Bonfiglioli) (Hybrid Systems LLP)

(DETA) (Siemens) (AW)

(Parkers) (Siemens) (ZF)

(picture: Pelamis)

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Use Case Cycle time range

Yield calculation Minutes - hours

Operation control Seconds

Reliability Milliseconds -seconds

Graded models:

Level 1: transient values

Level 2: effective values

Level 3: power flux

=> Optimized models, adapted to use case

• Vibrations,

• Failure scenarios

• Switching operations

• Annual yield calculation

• Daily course investigations

Graded Models

Level 1 model for synchronous generator

Level 3 model for synchronous generator

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Interface

Balance variables

ForceVelocity

Rotation speedTorque

Voltage Current

Candidate tools:

Matlab/Simulink

Simplorer

Modellica

Force / counterforce

Velocity

physical behaviour of a multi-body system

Generic interface

(picture: Ocean Energy)

(picture: Kymaner)

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Simulation Tasks

• Design of interface

• Choose simulation tools

• Development of component models (if necessary)

• Integration into overall model

• Application of model to WEC

Funded by

The International Research Alliance

03-09-2010