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Hybrid System Performance Evaluation

Henrik Bindner, Tom Cronin, Per Lundsager, Oliver Gehrke

Risø National Laboratory, Roskilde, Denmark

EWEC, 2nd March 2006, Athens

www.risoe.dk

Hybrid System Performance Evaluation

Hybrid Systems – the Problem

How will SYSTEM 1 perform at SITE 1?

Is SYSTEM 1 better than SYSTEM 2 at SITE 2?

Can you trust the answers?

Key Issue:

Develop method for system performance assessment

Main ingredient:

System modelling, especially supervisory controller modelling

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Hybrid System Performance Evaluation

This Work – the Questions

The presentation deals with the following issues of modelling of hybrid system:

The optimum timestep to adequately take account of the wind variability.

Sensitivity of various performance criteria to the choice of timestep. The nature of controller approximations necessary for longer

timesteps.

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Hybrid System Performance Evaluation

This Work – the Approach

• Model simple system with 2 diesel gensets, 3 wind turbines and 3 loads

• Specify performance criteria

• Investigate performance for 2 different controllers and for 3 different simulation time steps

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Hybrid System Performance Evaluation

IPSYS – an explanation

IPSYS is a flexible framework for simulation of integrated energy systems

• IPSYS is a dispatch model - modelling timesteps are in the range 10s-60min

• IPSYS explicitly models the power system and does load sharing between the frequency controlling units

• IPSYS is multi-domain – it models the electrical, mechanical, thermal, water or other domains

• IPSYS is very flexible in modelling configurations and supervisory controllers

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Hybrid System Performance Evaluation

Layout of the Simulated Hybrid System

G

Combined Load 1

Combined Load 2

Combined Load 3WTG WTG WTG

DumpLoad G

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Hybrid System Performance Evaluation

Main System Details

2 x diesel generators: 780kW

Generation voltage: 400V

Step-up transformer: 1.7MVA

Distribution voltage: 22kV

3 x 300kW wind turbines

No-load reactive power compensation: 250kVA

900kW dump load

3 x geographically dispersed loads

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Hybrid System Performance Evaluation

Load Profiles

0 2 4 6 8 10 12 14 16 18 20 22 240

100

200

300

400

500

600

Time (hours)

Act

ive

Po

wer

(kW

)

Load 1Load 2Load 3

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Hybrid System Performance Evaluation

Droop Curve for Diesel Generators and Dump Load

48

48.5

49

49.5

50

50.5

51

51.5

0 200 400 600

Power (kW)

Fre

qu

ency

(H

z)

Diesel generator

Min system load

Dump load

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Hybrid System Performance Evaluation

Diesel Generator Controls

100

200

300

400

500

600

Act

ive

Po

wer

(kW

)

100

200

300

400

500

600

Time

Rea

ctiv

e P

ow

er (

kVA

r)

ON: 75% Pr = 570kW

OFF: 25% Pr = 195kW

ON: 75% Qr = 510kVAr

OFF: 25% Qr = 170kVAr

Threshold Controller Margin Controller

Reserve Capacity =

(α × load kW) + (β × wind kW)

Controller turns on another diesel if present generator cannot meet the current load plus the Reserve Capacity.

Controller turns diesel off if it is not needed to meet the current load plus the Reserve Capacity.

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Hybrid System Performance Evaluation

Diesel Generator Fuel Curve

0 200 200 600 8000

50

100

150

200

Power (kW)

Fu

el C

on

sum

pti

on

(l/h

r)

No-load offset

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Hybrid System Performance Evaluation

Graphical Output from IPSYS

0 5 10 15 20 25 30-1500

-1000

-500

0

500

1000

1500

Time (days)

Po

wer

(kW

)

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Hybrid System Performance Evaluation

Running of the Diesel Generators

0.5 1 1.5 2 2.5 3 3.5 4

x 104

0

500

DG

1

5 10 15 20 25 300

500

DG

2

500 1000 1500 2000 2500 3000 3500 40000

500

DG

1

5 10 15 20 25 300

500

DG

2

100 200 300 400 500 600 7000

500

DG

1

0 5 10 15 20 25 300

500

Time (days)

DG

2

1 min

10 min

60 min

Act

ive

Pow

er (

kW)

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1 10 600

20

40

60

80

100

120

Simulation Timestep (minutes)

No

of

star

tsDiesel Generator No.2 Starts

25/75%

30/80%

35/85%

25/85%

1 10 600

100

200

300

400

500

600

700

Simulation Timestep (minutes)

Ho

urs

Diesel Generator No.2 Runtime

Hybrid System Performance Evaluation

Numbers of Starts for Diesel No. 2 and Hours Run

1 10 600

20

40

60

80

100

120

Simulation Timestep (minutes)

No

of

star

ts

Diesel Generator No.2 Starts

25/75%

30/80%

35/85%

25/85%

1 10 600

100

200

300

400

500

600

700

Simulation Timestep (minutes)H

ou

rs

Diesel Generator No.2 Runtime

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Hybrid System Performance Evaluation

IPSYS Outputs for this Assessment

• Total energy generated during the simulation

• Wind energy generated

• Wind usage

• Wind share

• Dump load share

• Diesel generator starts

• Diesel generator run time

• Total diesel fuel used

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Hybrid System Performance Evaluation

Simulation Cases Investigated

Base Case

Threshold Controller & Raw Wind Input

Threshold Controller with min runtime adjustments

& Raw Wind Input

Threshold Controller & Filtered Wind Input

All simulations run with 1, 10 & 60 minute timesteps

Margin Controller & Raw Wind Input

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Hybrid System Performance Evaluation

Accuracy is necessary in modelling limits in even simple controllers.

1 10 600

200

400

600

800

Simulation Timestep (minutes)

Die

sel R

un H

ours

1 10 600

100

200

300

400

500

600

700

Diesel Generator No.2 Runtime

Simulation Timestep (minutes)

Hou

rs

1 10 600.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2x 10

5 Total Fuel Used

Simulation Timestep (minutes)

Litr

es

alpha 5%, beta 85%

alpha 5%, beta 50%

alpha 30%, beta 50%

1 10 600

50

100

150

200

Simulation Timestep (minutes)

No

of s

tart

s

Diesel Generator No.2 Starts

1 10 600

200

400

600

800

Simulation Timestep (minutes)

Die

sel R

un H

ours

1 10 600.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2x 10

5 Total Fuel Used

Simulation Timestep (minutes)

Litr

es

25/75%

30/80%

35/85%

25/85%

Both controllers show a sensitivity to a change

in limits

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Hybrid System Performance Evaluation

….but the timestep can influence the effect.

1 10 600

50

100

150

Simulation Timestep (minutes)

Die

sel N

o. o

f Sta

rts

1 10 600

100

200

300

400

500

600

Simulation Timestep (minutes)

Die

sel R

un H

ours

1 minute minimum run

30 minute minimum run

60 minute minimum run

The effect of changing the minimum run time is reduced as the timestep is increased.

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Hybrid System Performance Evaluation

Timestep impact on long-term performance indicators is relatively small

1 10 600

50

100

150

200Diesel Generator No.2 Starts

Simulation Timestep (minutes)

No

of s

tart

s

1 10 608

8.5

9

9.5

10

10.5

11x 10

4

Simulation Timestep (minutes)F

uel C

onsu

mpt

ion

(litr

es)

1 minute minimum run

30 minute minimum run

60 minute minimum run

1 10 600

100

200

300

400

500

600

700

Diesel Generator No.1 Runtime

Simulation Timestep (minutes)

Hou

rs

1 10 600

500

1000

1500Total Diesel Generator Runtime

Simulation Timestep (minutes)

Hou

rs

1 10 608

8.5

9

9.5

10

10.5

11x 10

4

Simulation Timestep (minutes)

Fue

l Con

sum

ptio

n (li

tres

)

alpha 5%, beta 85%

alpha 5%, beta 50%

alpha 30%, beta 50%

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Hybrid System Performance Evaluation

Major impact of timestep is on diesel start/stops

1 10 600

50

100

150

200

Simulation Timestep (minutes)

No.

of s

tart

s

1 10 600

50

100

150

Simulation Timestep (minutes)N

o of

sta

rts

25/75%

30/80%

35/85%

25/85%

1 10 600

100

200

300

400

500

600

700

Diesel Generator No.1 Runtime

Simulation Timestep (minutes)

Hou

rs

1 10 600

500

1000

1500Total Diesel Generator Runtime

Simulation Timestep (minutes)

Hou

rs

1 10 608

8.5

9

9.5

10

10.5

11x 10

4

Simulation Timestep (minutes)

Fue

l Con

sum

ptio

n (li

tres

)

alpha 5%, beta 85%

alpha 5%, beta 50%

alpha 30%, beta 50%

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Hybrid System Performance Evaluation

Impact of Wind Sampling Period (1)

0 50 100 150 2003

4

5

6

7

8

9

10

Time (minutes)

Win

d S

peed

(m

/s)

1 minute timeseries

10 minute filtered

60 minute filtered

Raw Wind Data Series

0 5 10 15 200

50

100

150

200

250

300

350

400

0 5 10 15 200

50

100

150

200

250

300

350

400

Power Frequency

Filter

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Hybrid System Performance Evaluation

Impact of Wind Sampling Period (2)

1 10 600.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2x 10

5

Timestep (mins)

Fue

l Con

sum

ptio

n (li

tres

)

Raw 25/75Raw 30/80Raw 35/85Raw 25/85Filt 25/75Filt 30/80Filt 35/85Filt 25/85

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Hybrid System Performance Evaluation

Conclusions

• Simulation timestep has only a limited impact on overall system performance in terms of fuel consumption and wind usage

• Simulation timestep has a significant impact on operating conditions of components e.g. number of start/stops of genset

• Wind filtering has only minimal impact on fuel consumption

• For feasibility studies long timesteps (1h) give results of adequate accuracy

• Short timesteps (1min) are necessary for study of controllers and interaction between components, component operating conditions and wear and tear

• It is important to model reactive power aspect of controllers, as this has a considerable impact on the system operation and simulation results.

• Short time steps will allow real controllers to be implemented in simulation tool – IPSYS is designed for that

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Hybrid System Performance Evaluation

Limitations on Results

• Only one hybrid system configuration has been simulated.

• No storage included in studied configuration.

• Only simple controllers investigated.

• System parameters were adjusted to ensure all runs at all timesteps would run – this could hide the full of impact of timestep changes.

• Only a short step towards system testing – Lots of work required