Variable speed control of wind turbines based on the quasi ...
Dynamic Analysis of Fluid Power Drive-trains for Variable Speed Wind Turbines
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Transcript of Dynamic Analysis of Fluid Power Drive-trains for Variable Speed Wind Turbines
1Challenge the future
Dynamic Analysis of Fluid Power Drive-trains for Variable Speed Wind TurbinesA parameter study
Antonio Jarquín Laguna, Niels Diepeveen
4th February 2013
2EWEA 2013
Fluid power drivetrains
Torque Pressure difference
Rot Speed Volumetric flow rate
--------------------------------------------------Mech Power Hydraulic Power
Artemis - proprietaryHagglunds- proprietary
3EWEA 2013
Fluid power drivetrains
•Not a new idea i.e. different projects in the 80’s
•What has changed?
•New interest by several parties around the world
•Different concepts
Some background
1,3 MW BENDIX/Shackle project (USA)
4EWEA 2013
Why use hydraulics transmissions in WE?Some benefits
• Continuous variable transmission ratio is possible
-> use of synch generator, -> eliminate most of power electronics
• High torque to weight ratio (compact)
-> lighter nacelle -> reduce structural steel
• Modular-> ease for maintenance and
replacement
• Construction material is steel -> not copper or rare earth materials
• Efficiency is still the main concern
-> Hydraulic solutions still offer solid economic benefits
• Limited availability of multi MW components
-> so far no commercial need
• Without a track record in WE -> more prototypes and public data
is needed
Main challenges
5EWEA 2013
Possible configurations
Nacelle solution
Tower based solution
6EWEA 2013
How to evaluate the dynamic performance?This research
•Present a dynamic model of a fluid power transmission and its control for variable speed turbines
•Parametric study through numerical simulations
• Hydraulic line length
• Oil internal leakages in hydraulic drives
• Rotor mass moment of inertia
7EWEA 2013
Approach
External controller interface (DLL)
Standard industry software: GH Bladed
8EWEA 2013
Parameter study for a 5MW turbine
1)Define reference properties
-> Flow rate: 10, 000 lpm
-> Pressure: 350 bar
Use the same rotor as the NREL 5MW turbine reference
NREL 5MW rotor parametersRotor diameter: 126 mMax tip speed: 80m/sRated rotor speed: 12,1 rpmRated wind speed: 11,4 m/s
0 5 10 15 20 250
1000
2000
3000
4000
5000
6000
7000
Po
wer
[kW
]
Mech power rotor shaft
Hydraulic power pump side
Mech power generator shaft
0 5 10 15 20 250
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wind speed [m/s]
Eff
icie
nci
es [
-]
Pump
PipelineMotor
Total
0 5 10 15 20 250
1000
2000
3000
4000
5000
To
rqu
e [k
Nm
]
Ideal
Real
0 5 10 15 20 250
5000
10000
Vo
lum
etri
c fl
ow
rat
e [l
pm
]
Ideal
Real
0 5 10 15 20 250
100
200
300
400
Pre
ssu
re [
bar
]
Work pressure
Charge pressure
0 5 10 15 20 250
0.5
1
Wind speed [m/s]
Mo
tor
rela
tive
d
isp
lace
men
t [-
]
9EWEA 2013
Length of hydraulic line
0 50 100 150 200 250 3000
100
200
300
400
Time[s] P
um
p p
ress
ure
[b
ar]
L= 10 m
L= 20 mL= 50 m
L= 100 m
0 50 100 150 200 250 3004
6
8
10
12
14
Time[s]
Ro
tor
spee
d [
rpm
]
More oil in the system leads to higher fluid inertia
Max pressure overshoots:
10 m: 1%20 m: 2%50 m: 20%100m: 40%
Step inputs are not realistic! but they are useful to indicate the system performance
0 50 100 150 200 250 3000
2
4
6
8
10
12
Time [s]
Win
d s
pee
d [
m/s
]
10EWEA 2013
Hydraulic motor volumetric efficiency
0 50 100 150 200 250 3004
6
8
10
12
14
Time[s]
Ro
tor
spee
d [
rpm
]
0 50 100 150 200 250 3000
100
200
300
400
Time[s] P
um
p p
ress
ure
[b
ar]
vol,m
= 60%
vol,m
= 80%
vol,m
= 90%
vol,m
= 95%
Oil internal leakages introduce damping:
Max pressure overshoot:
Efficient hydraulic motor 50%
Inefficient hydraulic motor30%
Using long hydraulic line (100 m)
0 50 100 150 200 250 3000
2
4
6
8
10
12
Time [s]
Win
d s
pee
d [
m/s
]
Step inputs are not realistic! but they are useful to indicate the system performance
11EWEA 2013
Rotor mass moment of inertiaInertias representative for a rotor 10 times lighter (light grey) / heavier (black)
Comparison of inertias in terms of rotor diameter
80m- 2MW 126m- 5MW200m-12,5MW 0 100 200 300 400 500 600
6
8
10
12
14
Time [s]
Ro
tor
spee
d [
rpm
]
0 100 200 300 400 500 6000
100
200
300
400
Time [s]P
um
p p
ress
ure
[b
ar]
Jr= 3.88e6 kgm2
Jr= 3.88e7 kgm2
Jr= 3.88e8 kgm2
0 100 200 300 400 500 6004
6
8
10
12
Time [s]
Win
d s
pee
d [
m/s
]
Hub height wind speed of 8 m/s 17.67% TI
12EWEA 2013
Summary
• A fluid power transmission model and control is presented for variable speed turbines (details are found in full paper).
• Friction losses are minor for laminar flow
• Long hydraulic lines are prone to higher pressure fluctuations with the proposed control strategy
• Minor damping provided by low volumetric efficiency of the motor
• Higher inertias lead to slower and smoother response
13EWEA 2013
Outlook for fluid power transmissions • First prototypes of multi-MW wind
turbines with fluid power transmission are being built/tested
• Research at TUDelft:• Centralized electricity generation
through fluid power transmission• Energy storage opportunities using
hydraulic transmission• Opportunities for water hydraulics
Generator platform
MicroDOT 10kW demonstrator @ TU
Delft
MicroDOT 10kW demonstrator @ TU
Delft
14EWEA 2013
Capital expenditureEstimations of the impact of fluid power drivetrains
• CAPEX €/kW
-> 24% steel reduction in tower and foundation -> 7,7% CAPEX reduction
-> Elimination of power electronics -> 2,9% CAPEX reduction
-> Turbine installation cost reduction of 10% -> 0,9% CAPEX reduction
Overall CAPEX reduction: 11,5%
Arapogianni A, Moccia J. “Economics of Wind Energy”, Modern Energy Review, Vol. 4-2, 2012, pp. 22-28.
Capital costs OffshoreTurbine 51%Grid/electrical systems 9%Foundation 19%Installation of turbine 9%Electric installation 6%Consultancy/management 4%Financial/ insurance costs 2%
15EWEA 2013
Operational expenditureEstimations of the impact of fluid power drivetrains
• OPEX €/kWh
-> Maintenance (service and spare parts) cost reduction of 30%
Overall OPEX reduction: 11,7%
Arapogianni A, Moccia J. “Economics of Wind Energy”, Modern Energy Review, Vol. 4-2, 2012, pp. 22-28.
Maintenance (Service and spare parts) 39%Port activities 31%Operation 16%License Fee 3%Other costs 12%
Share of Operation and Maintenance Costs
Offshore wind
16EWEA 2013
Annual energy productionEstimations of the impact of fluid power drivetrains
• AEP kWh/year
-> Using a 5 MW rotor (NREL reference turbine)
-> 10 m/s average wind speed in the North Sea
-> Same availability as reference turbine
-> Capacity factor of 0,32-0,33 (reference of 0,35)
Overall energy production reduction: 4,7 to 8,6%
17EWEA 2013
89.62
83.1580.46
77.52
70
75
80
85
90
95
Current gearedsolution
Hydraulictransmission
0,32 Cap factor
Hydraulictransmission
0,33 Cap factor
Hydraulictransmission
0,35 Cap factor
LCOE offshore wind (€/MWh)
Cost of energy for multi-MW wind turbinesEstimations of the impact of fluid power drivetrains
•Levelised Cost of Energy Reference value for offshore wind is 89,62 €/MWh
-> Standard hydraulic motor(90% vol efficiency, reference):Capacity factor of 0,32 83,15 €/MWh ->7,2% cost reduction
-> High efficiency hydraulic motor (95% vol efficiency, likely):Capacity factor of 0,33 80,46 €/MWh ->10,2% cost reduction
-> Same energy production as reference:Capacity factor of 0,35 77,5 €/MWh ->13,5% cost reduction
European Wind Energy Association “Online Electricity Cost Calculator”, Available at: www.ewea.org/index.php?id=201 (accessed December 2012)
18EWEA 2013
Thank you for your attention!
Questions?
19EWEA 2013
Block diagram of dynamic system
Detailed models are described in full paper
20EWEA 2013
Pipelines dynamics
0 10 20 30 40 50 60 70 80 90 100-0.5
0
0.5
1
1.5
2
Normalized time c*t/L
Dow
nstr
eam
Pre
ssur
e [P
a]
unsteady friction
steady friction
Blocked line response to pressure step input; Dissipation number Dn=0,01
Distributed parameter model
Dissipative model
•Includes unsteady friction viscous effects
•Better description of transient behavior
•Reduced order models ideal for time-domain simulations
•Based on the work of Makinen[1]
[1] Makinen J, Piché R, Ellman. “A Fluid TransmissionLine Modeling Using a Variational Method”, ASME Journal of Dynamic Systems Measurement and Control, Vol. 122, 2000, pp. 153-162.
21EWEA 2013
Variable speed control strategy
2 4 6 8 10 12 14 160
1000
2000
3000
4000
5000
11.4 m/s
11 m/s
10 m/s
9 m/s
8 m/s
4,000 kW 5,000 kW 6,000 kW
Rotor speed [rpm]
To
rqu
e [k
Nm
]
Pressure PI control loop with outer speed feedback
Minimum rotor speed no longer limited by generator
Transition region, similar to geared solution
NREL 5MW rotor parameters
Rated pressure: 350 bar (15 bar charge pressure)
Max tip speed: 80m/sRated rotor speed: 12,1 rpmUrated: 11,4 m/s
22EWEA 2013
Transmission efficiency[2]
[2] Jarquin Laguna A, Diepeveen N. “The Rise of Fluid Power Transmission Systems for Wind Turbines ”, Modern Energy Review, 2012, Vol. 4-2, pp. 64-68,.
23EWEA 2013
NREL Cp –Ct lambda curve
0 2 4 6 8 10 12 14 16 180
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Cmax
max
C
[-]
0 2 4 6 8 10 12 14 16 180
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
CP
max
P
max
Tip speed ratio [-]
CP [-
]
Max Cp= 0,485 @ lambda=7,55 pitch=0 deg