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