Wind Power Generation Power Flow and Dynamic · PDF fileWind Power Generation Power Flow and...

NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC

Eduard MuljadiNREL, Golden [email protected]

UWIG-EnerNexModeling Workshop

Albany, NYJuly 5-6, 2011

Wind Power Generation Power Flow and Dynamic Modeling

Vadim ZheglovEnerNex, Tennessee [email protected]


Background


Conventional vs. Wind Power Plant

GSUXfmr

Large Synchronous

Generator

PrimeMover

POI or connection to the grid Collector System

Station

Feeders and Laterals (overhead and/or underground)

Individual WTGs

Interconnection Transmission Line

Other Conv.Generator

LoadLoad

POI or Point of Interconnection Collector

SystemStation

InterconnectionTransmission Line

Feeders and Laterals (overheadand/or underground)

Individual WTGs


Power GenerationConventional vs Wind Power Plant

• Many (hundreds) of wind turbines (1 MW – 5 MW each)

• Prime mover: wind (wind turbine) –renewable (free, natural, pollution free)

• Controllability: curtailment

• Predictability: wind variability based on wind forecasting, influenced more by nature (wind) than human, based on maximizing energy production (unscheduled operation).

• Located at wind resource, it may be far from the load center.

• Generator: Four different types (fixed speed, variable slip, variable speed, full converter) –non synchronous generation

• Type 3 & 4: variable speed with flux oriented controller (FOC) via power converter. Rotor does not have to rotate synchronously.

• Single or multiple large (100 MW) generators.

• Prime mover: steam, combustion engine – non-renewable fuel affected by fuel cost, politics, and pollution restrictions.

• Controllability: adjustable up to max limit and down to min limit.

• Predictability: preplanned generation based on load forecasting, influenced by human operation based on optimum operation (scheduled operation).

• Located relatively close to the load center.

• Generator: synchronous generator

• Fixed speed – no slip: flux is controlled via exciter winding. Flux and rotor rotate synchronously.


Four basic topologies based on grid interface:– Type 1 – conventional induction generator– Type 2 – wound-rotor induction generator with variable rotor

resistance– Type 3 – doubly-fed induction generator– Type 4 – full converter interface

generator

full power

PlantFeeders

actodc

dctoac

generator

partial power

PlantFeeders

actodc

dctoac

generator

Slip poweras heat loss

PlantFeeders

PF controlcapacitor s

actodc

generator

PlantFeeders


Type 1 Type 2 Type 3 Type 4

Power Generation

Types of Wind Turbine Generator


Power Flow ModelingWind Turbine Generator


WPP Representation


Station


Individual WTGs


Collector System Equivalent

jXeqReq

Beq/2 Beq/2


Equivalencing


Equivalencing


Pad-MountedTransformer


Reactive Compensations

Represented bySeparate Model

Type 1 and 2 WTGs are induction machines:

• Several stages of capacitors banks at the WTG terminals are normally applied . Net power factor at bus 5 ~ 1.0

• In power flow: • modeled as fixed shunt devices• WTG of type 1 is approximately PF=0.9 therefore the capacitor need is about to be ½ of the power output. • example, for a 100 MW WPP at full output, Qmin = Qmax = -50 Mvar• and add a 50 Mvar shunt capacitor at the WTG terminals.

• Plant level reactive compensation may still be installed to meet interconnection requirements and should be explicitly represented in power flow.



Type 3 and Type 4 WTGs (an estimate to start depending on the terminal voltage)

• These WTGs are capable of adjusting power factor to a desired value within the rating of the generator and converter. They are also capable of voltage control at the interconnection point or at its terminals.

• External reactive power compensation is often required to meet interconnection requirements

• If these WTGs do not participate in voltage control, the equivalent generator should be assigned a fixed power factor, typically unity. (i.e., Qmin = Qmax = 0).

• If the WTGs do participate in voltage control, then the equivalent generator should be assigned a reactive capability approximately equal to the aggregate WTG reactive power range (i.e., Qmin = -Srated tan(cos-1(0.90); and Qmax = Srated tan(cos-1(0.95)) ).

• For example, consider a 100 MW WPP that employs Type 4 WTGs with specified power factor range +/-0.95 at full output. In this example, Qmin should be set to -33 Mvar and Qmax should be set to +33 Mvar. At an output level below rated, the reactive limits should be adjusted according to the WTG capability curve.


Reactive PowerFlow

+

VA

-

jI X+

VB

-

VA = VB

QA =QB= 0.5 I2X

A

B

A = B

All Q comes from A

QA =I2X ; QB= 0

VA > VB ; B = 0 VB = 1.0

VA

jI XI

QB =I2X ; QA= 0

VA < VB; A = 0VB = 1.0

VA

jI XIA B

VA

II”

VA”VA

II’

VA’

VB = 1.0 VB”= 1.1

Equal Q (VAR) contribution

All Q comes from B

Overexcited VA’ > VA ; QA =I’2X ; QB< 0

I

VA= 1.0

jI XI

VB = 1.0



Station


Individual WTGs


X100 > X1

IX100 > IX1


Turbine far from substation

Turbine close to substation


Practical Limit of Reactive Power Output

• Due to collector system effects, some WTGs in the WPP will actually reach terminal voltage limits before reaching the nameplate reactive power limits.

• The net effect is that actual reactive power capability could be less than the nameplate.

• The reactive power capability can be determined by field test or careful observation of WPP performance during abnormally high or low system voltage.

• For example, Figure 7 shows the results of field tests to determine the practical reactive limits of a 200 MW WPP.

• All measurements were made at the interconnection point. Taking into account the effect of transformer and collector system impedances, the reactive power limits of the equivalent WTG can be established.

• Currently, there are no industry standard guidelines for testing WPP steady-state reactive limits.


+95 and


reactor

VPOI

I

VAVinf



VPOI

I

VAVinf


P34.5 kV

Q34.5 kV

QWT = 0.435 0 -0.4353-phase fault, all WTGs at 12 m/sec

From « Validation of the WECC Single-Machine Equivalent Power Plant », Presented DPWPG-WG Meeting at IEEE PSCE, March 2009 - Jacques Brochu, Richard Gagnon, Christian Larose, Hydro Quebec

Detailed Vs. Single-Machine Representations

Validation


ValidationDetailed Vs. Single-Machine Representations

From « Validation of the WECC Single-Machine Equivalent Power Plant », Presented DPWPG-WG Meeting at IEEE PSCE, March 2009 - Jacques Brochu, Richard Gagnon, Christian Larose, Hydro Quebec

P34.5 kV

Q34.5 kV

0.435 0 -0.435

4 feeders = Typical

1 and 2 feeders

2 and 4 feeders = Typical

1 feeder

QWT =3-phase fault, different wind speed for each feeder


Wind Power PlantNetwork

Gen

100 MW equivalent wind turbine generator

Infinite Bus

Ideal Gen

230 kV Line 1

R1, X1, B1

230 kV Line 2

R2, X2, B2

34.5 kV collector system equivalentRe, Xe, Be

0.6/34.4kV equivalent GSU transformer

Rte, Xte

34.4/230 kV station transformer

Rt, Xt.

Station‐level shunt compensation

Turbine‐level shunt compensation

21 34

5


Power Flow

Power Flow

• Prepare the network (line branches, transformers, generators, and the loads).

• Set the level of the loads and generations.

• For wind turbine generator:• Type 1 and 2 – set the level of real power and reactive power, set the maximum and minimum limits of the real and reactive power. set the level of capacitor compensation.• Type 3 and 4 – set the level of real power and reactive power, and set the maximum and minimum limits of real and reactive power

• Run the power flow program

• Observe the abnormal operation (over load lines, over/under voltage buses and make adjustments as necessary.

• Repeat the process for different scenarios: load change, generation change, line disconnected


Power FlowData


Power FlowAssessment

Gen


Infinite Bus

Ideal Gen

230 kV Line 1

R1, X1, B1

230 kV Line 2

R2, X2, B2



Rte, Xte


Rt, Xt.



21 3

4

5

Fault Event

Pre‐fault Condition

Post‐fault Condition

Gen


Infinite Bus

Ideal Gen

230 kV Line 1

R1, X1, B1

230 kV Line 2

R2, X2, B2



Rte, Xte


Rt, Xt.



21 3

4

5


Post‐fault Condition

Power FlowAssessment

Pre‐fault Condition


Dynamic ModelingWind Turbine Generator


Dynamic ModelingNeeds

Dynamic models are needed to study the dynamic behavior of power system. Users include system planners and operators, generation developers, equipment manufacturers, researchers, and consultants.

Wind Power Plant (WPP) models are needed to study the impact of proposed or existing wind power plants on power system and vice versa (i.e. to keep voltage and frequency within acceptable limits).

Models need to reproduce WPP behavior during transient events such as faults/clear events, generation/load tripping, etc.

G1G2

G3

WTGwind turbine generator

newline

lossofline

Resizing

ShortCircuit


Dynamic ModelingCheck List

Check List:

• Prepare the power flow model and run the power flow to ensure that the pre-fault and post-fault condition results are acceptable and makes sense.

• For wind turbine generator:• Prepare the wind turbine dynamic model to be represented• If the wind turbine parameters (of the WECC generic models) are not available from the turbine manufacturers, use the default data provided by the generic models available from the WECC website• If the wind turbine parameters (of the WECC generic models) of the turbines to be simulated are available from the turbine manufacturers, use the latest model parameters provided.

• Prepare the dynamic script of the scenario of interests and run the dynamic simulation for the contingencies fault, loss of lines, etc.) to be investigated.


Dynamic ModelingTime Scale

Switching Transients

Subsynchronous Resonance

Transient Stability

Oscillatory Stability

Long-term Dynamics

TIME (seconds)

10-6 10-5 10-4 .001

1 cycle

104.1 1 10 100 1000

1 minute 1 hour

.01

Source: Dynamic Simulation Applications Using PSLF – Short Course Note – GE Energy


Dynamic ModelsWECC Generic Models

Generic model development in PSSE/PSLF– Complete suite of prototype models implemented

Current focus– Model validation & refinement (e.g., freq. response)– Identification of generic model parameters for different

manufacturers (at NREL)

Model Type Type 1 Type 2 Type 3 Type 4Generator wt1g wt2g wt3g wt4gExcitation / Controller wt2e wt3e wt4eTurbine wt1t wt2t wt3t wt4tPitch Controller wt1p wt2p wt3p wt4p

Generic model WT1 WT2 WT3 WT4Generator WT1G WT2G WT3G WT4GEl. Controller WT2E WT3E WT4ETurbine/shaft WT12T WT12T WT3TPitch control WT3PPseudo Gov/: aerodynamics WT12A WT12A

PSLF

PSSE


Dynamic ModelsWTG Type 1 and 2

generator

Slip poweras heat loss

PlantFeeders


actodc

generator

PlantFeeders


Type 1 WTG Type 2 WTG


Dynamic ModelsWTG Type 3 and 4

generator

partia l power

PlantFeeders

actodc

dctoac

generator

full power

PlantFeeders

actodc

dctoac

Type 3 WTG Type 4 WTG


Single TurbineRepresentation

W

Pad-mounted Transformer Equivalent

Wind Turbine Generator Equivalent

PF CorrectionShunt Capacitors

Collector System

Equivalent


-Plant-level Reactive Compensation

POI or Connection to the Transmission

System

Station Transformer(s)

Major components of WPP Equivalent Representation:

• Wind Turbine Generator (WTG) Equivalent and power factor correction (PFC) caps• Plant level reactive power compensation if applicable• Pad-mounted Transformer Equivalent• Collector System Equivalent branch.


Multiple Turbine Representation

In some cases, multiple turbine representation may be appropriate, for example:

• To represent groups of turbines from different types or manufacturers

• To represent a group of turbines connected to a long line within the wind plant

• To represent a group turbines with different control algorithms.

W

Pad-mounted Transformer

Equivalent #2

WTG Equivalent #2 Type 1

PF CorrectionShunt Capacitors

Collector System Equivalent #2



System


W


Equivalent #1

WTG Equivalent #1 of Type 3 Voltage controlledCollector System Equivalent #1 considered to

be a long/weak line feeder

W


Equivalent #3WTG Equivalent #3 of Type 3 PF=1

Collector System Equivalent #3

21 MW

34 MW

45 MW

Total Output100 MW


Dynamic ModelValidation

•Prepare the simulation carefully (i.e. the correct information must be used): type of WTG, collector system impedance, transformers, power system network, input parameters to dynamic models, control flags settings set-up, reactive power compensation at the turbine level or at the plant level.

•Initialize the simulation based on pre-fault condition (check v, i, p, q, f, if available).

•Recreate the nature of the faults if possible, otherwise use the recorded data to drive the simulation and compare the measured output to the simulated output (pre-fault, during the fault, post-fault).

•Represent the events for the duration of observation (any changes in wind, how many turbine were taken offline due to the fault?).

•Prepare the data measured to match the designed frequency range of the software used.

•Field data is expensive to monitor, public domain data is limited, difficult to get, and quality of data needs to be scrutinized

– Anticipate errors in the measurement and make the necessary correction– The location of simulation should be measured at the corresponding monitored data.


Dynamic ModelValidation Example

Example of Dynamic ModelSimulation versus Field Data (Type 3)

W

Pad-mounted Transformer Equivalent

91% WTGs stays “on” after the fault.

Collector System

Equivalent



System


W 9% WTGs were dropped of line during the fault.

Two Turbine Representation



System


136 WTGs were represented

9% WTGs were dropped of line during the fault.

Complete Representation (136 turbines)



V and f

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2Time (s)

Volta

ge (p

.u.)

0.95

0.99

1.03

1.07

1.11

1.15

Freq

uenc

y (p

.u.)

Vf

Real Power Comparison

0

20

40

60

80

100

120

140

0 0.5 1 1.5 2 2.5 3 3.5 4Time (s)

Rea

l Pow

er (M

W)

P-sim-1wtg (MW)P-measured (MW)P-sim-136WTG

Reactive Power Comparison

-60

-40

-20

0

20

40

60

80

0 0.5 1 1.5 2 2.5 3 3.5 4

Time (s)

Rea

ctiv

e Po

wer

(MVA

R)

Q-sim-1wtg (MVAR)Q-measured (MVAR)Q-sim-136WTG

WWind TurbineGeneratorEquivalent

InputV and f

A C BSystem Generator

Compare P&Q measured to P&Q simulatedV and f

Regulated Bus


Dynamic ModelValidation

•Another method to validate new model is to use another model that has been validated against field measurement as a benchmark model.

•Several transient fault scenarios can be performed using both models, and the results can be compared.

•Parameter Tuning– The new model and the benchmark model may have some differences in

implementation, we may have to perform parameter tuning to match the output of the benchmark model.

– However, one should realize that the model may not be able to match the output of the benchmark model in all transient events.

•Parameter Sensitivity– In order to limit the number of parameters that should be tuned, parameter

sensitivity analysis may need to be performed.– In general important parameters are varied one by one and the sensitive

parameters can be tuned to match the bench mark model.

Comparison against other model (Benchmarking)



Terminal Voltage Real Power

Reactive PowerTurbine Speed

Example of Model to Model Comparison (Type 2 “Detailed” Model vs Generic Model)


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