Developing Models for Wave Energy Conversion
Systems
Ted Brekken, Asher Simmons, Annette von Jouanne
School of Electrical Engineering and Computer Science
Oregon State University
Corvallis, Oregon
July 30 2014
2014 IEEE Power and Energy Society
General Meeting
July 30 2014
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Outline
Overview
Examples of WECs
Power Take Off
Power Characteristics
WEC Modeling
Large Scale Modeling
Summary and Recommendation
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Ocean Wave Energy Overview
I
Potential and kinetic energy in water particle motion,
particularly in large swells
I
Significant resource for large land masses with a large western
coast
I
In the U.S., the total resource is estimated at to be similar to
the total hydro resource (approx. 6%)
I
Multiple device designs
I
Generally characterized by slow speed (e.g., 1 m/s) and large
forces (e.g., 1 MN)
I
High power density: 30 kW/m (compared with 150 W/m2 for
PV and 600 W/m2 for wind)
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Overview
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Wave Energy Conversion Overview
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Overview
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Section 2
Examples of WECs
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Examples of WECs
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Point Absorber
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Examples of WECs
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Point Absorber
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Examples of WECs
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Surge Converter
[www.aquamarinepower.com]
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Examples of WECs
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Oscillating Water Column
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Examples of WECs
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Oscillating Water Column
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Examples of WECs
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Attenuator
[www.pelamiswave.com]
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Examples of WECs
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Attenuator
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[www.pelamiswave.com]
Examples of WECs
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Overtopping
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Examples of WECs
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WEC Type Summary
There are many different WECs that operate in different ways with
different PTOs!
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Examples of WECs
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Section 3
Power Take Off
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Power Take Off
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Hydraulic: Pelamis
[www.pelamiswave.com]
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Power Take Off
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Hydraulic: Pelamis
[www.pelamiswave.com]
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Power Take Off
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Hydraulic: Pelamis
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Power Take Off
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Direct Drive: Columbia Power Technologies
[www.columbiapwr.com]
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Power Take Off
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Direct Drive: Columbia Power Technologies
[www.columbiapwr.com]
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Power Take Off
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Direct Drive: Columbia Power Technologies
Power Take Off (PTO)
Power Take Off (PTO)
Electric Plant
Static DC Bus
1
AC/DC
Converter
2
AC/DC
Converter
3
AC/DC
Converter
4
AC/DC
Converter
DC/DC
Variable DC Bus
7
AC/DC
Converter
1
AC/DC
Converter
2
3
4
AC/DC
Converter
AC/DC
DC/DC
Converter
AC/DC
Converter
AC/DC
Converter
AC/DC
Converter
DC/DC
AC/DC
5
AC/DC
Converter
6
Static DC Bus
Capacitive Energy Storage
Burn
Resistor
Burn
Resistor
DC/DC
Line Inverter
Line Inverter
UL 1741 Rated
UL 1741 Rated
AC/DC
Converter
Converter
5
AC/DC
Converter
6
AC/DC
Converter
7
AC/DC
Converter
8
8
AC/DC
Converter
9
AC/DC
Converter
AC/DC
Converter
9
10
AC/DC
Converter
AC/DC
Converter
10
Station Power System
AC Bus
480 Vac
Collection System
XFMR
Auxiliary Shore
Power Connection
Inverter Control Power
Cooling System Power
Climate Control Power
AC Bus
120 Vac
SCADA Power
Isolation
Breaker
Emergency System Power
Navigation Power
Communications Power
AC Bus
480 Vac
MV XFMR
MV AC Bus
Umbilical Cable
Connection
UPS Converter
Station Battery
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Power Take Off
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Direct Drive: Seabased
[www.seabased.com]
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Power Take Off
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Direct Drive: OSU L10
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Power Take Off
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Direct Drive: OSU L10
0c]g
BSbVS`
>]eS`
ZW\S
4Z]Ob
=QSO\
TZ]]`
AbObW]\O`g
US\S`Ob]`
Q]WZa
AZWRW\U
[OU\Sb
OaaS[PZg
[Smithsonian]
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Power Take Off
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Limpet: Wells Turbine
[BBC]
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Power Take Off
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Limpet: Wells Turbine
[Voith]
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Power Take Off
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Power Take Off Summary
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There are many different WECs that operate in different ways
with different PTOs!
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Hydraulic, direct drive, induction generator, full-rated
converter
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Generally very high torque/force and low speed
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For direct-drive, speed and direction are variable
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Power Take Off
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Section 4
Power Characteristics
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Power Characteristics
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Power Characteristics
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Wave power varies on two primary timescales
I
I
Second-to-second (typical wave periods of 10 seconds for
ocean swells)
Hour-to-hour with changing sea state
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WEC power output dependent on control and amount of
energy storage
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Ratio of peak instantaneous power to average power can be
large
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Trade-off between higher average power and greater power
variability (including momentary negative power), thus higher
energy storage requirements.
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Power Characteristics
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Power Characteristics: Variable Amplitude and Frequency
200
150
100
volts
50
0
−50
−100
−150
−200
668
670
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674
676
seconds
Power Characteristics
678
680
682
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Power Characteristics: Variable Amplitude and Frequency
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Power Characteristics
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Power Characteristics: Pulse Power
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Power Characteristics
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Power Curves
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Very few power curves have been published.
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Operation in Region III (power shedding) is non-trivial and
may be different for each device.
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Definition of device power rating may be different for each
device.
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Power Characteristics
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Pelamis Power Curve
power (kW)
800
600
400
15
200
0
12
10
10
8
6
4
2
wave height (m)
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Power Characteristics
0
5
wave period (s)
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Section 5
WEC Modeling
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WEC Modeling
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Two Body WEC
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WEC Modeling
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Two Body WEC: WEC Dynamics
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WEC Modeling
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Two Body WEC: WEC Dynamics
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WEC Modeling
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Power: Optimal and Suboptimal
2
WEC position (optimal)
WEC position (suboptimal)
Water surface elevation
meters
1
0
−1
−2
0
10
20
30
seconds
40
50
60
6
1
x 10
PTO power (optimal)
mean PTO power (optimal)
PTO power (suboptimal)
mean PTO power (suboptimal)
Watts
0.5
0
−0.5
−1
0
10
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20
30
seconds
WEC Modeling
40
50
60
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Section 6
Large Scale Modeling
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Large Scale Modeling
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Large Scale Modeling
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Large Scale Modeling
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Large Scale Modeling
I
T.K.A. Brekken, T. Ozkan-Haller, and A. Simmons, “A
methodology for large-scale ocean wave power time-series
generation,” IEEE Journal of Oceanic Engineering, vol. 37,
no. 2, pp. 294–300, 2012.
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mz̈ = Fe + Fr + Fh + Fv + FPTO
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FPTO = −B v
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PPTO = −FPTO v
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Pelec = PPTO − Pstorage − Pconvloss − Pshed
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−Prated ≤ Pelec ≤ Prated
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Large Scale Modeling
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Large Scale Modeling
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Large Scale Modeling
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Large Scale Modeling
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Large Scale Modeling
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Section 7
Summary and Recommendation
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Summary and Recommendation
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Summary
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Wave energy technology is still developing
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Different PTO models may be necessary for different types of
WECs (e.g., point absorber, oscillating water column, etc.)
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WEC power output changes on at least two major timescales:
second-to-second (periodic) and hour-to-hour
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Ratio of peak power to average power may be high
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Full-rated converters most likely
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Energy storage may be inherent (hydraulics) or added on a
per-device, or per-array basis
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Summary and Recommendation
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Recommendation
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As of now, only a few large-scale ocean-tested WECs to go on
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Grid connected induction (WT1) and full-rated converter
(WT4)
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Energy storage function probably needs to be added
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Summary and Recommendation
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Prospective Block Diagram
power command
Hydrodynamics
Controller
∗
FPTO
Fe
WEC Model
FPTO
Power Take Off
(includes energy storage)
pos,speed
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Summary and Recommendation
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Thank you!
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Summary and Recommendation
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