WECC Model Validation Working Group

Denver, Colorado May 18-19, 2009

Wind Power Plant Wind Power Plant Dynamic Modeling and ValidationDynamic Modeling and Validation

Eduard MuljadiEduard.muljadi@nrel.gov

National Renewable Energy Laboratory Golden, CO

Abraham Ellisaellis@sandia.gov

Sandia National Laboratories Albuquerque, NM

Wind Power Plant (WPP) TopologyWind Power Plant (WPP) Topology

POI or connection to the grid Collector System

Station

Feeders and Laterals (overhead and/or underground)

Individual WTGs

Interconnection Transmission Line

BackgroundBackground((Dynamic Model of a Wind Power Plant)Dynamic Model of a Wind Power Plant)

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

Conventional Power Plant

Single Large (40MW to 1000MW+) generator

Prime mover: Steam, Combustion Engine – non-renewable fuel

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

Located where convenient for fuel and transmission access.

Generator: Synchronous Generator

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

Wind Power Plant

Many (hundreds) of wind turbines (1MW - 5MW each)

Prime mover: wind turbine - wind

Controllability: curtailment, ramp rate limit, output limit

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

Generator: Four different types (fixed speed, variable slip, variable speed, full converter)

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

Differences between Differences between Wind Power Plant and Conventional Power PlantWind Power Plant and Conventional Power Plant

Four basic types, based on the WTG technology:

Type 1 – Fixed-speed, conventional induction generators

Variable Slip WTG Type 2 – Induction generators with variable rotor resistance

Variable Speed WTGs Type 3 – Doubly-fed asynchronous generators with rotor-side converter Type 4 – Asynchronous generators with full converter interface

Wind Turbine Generator (WTG) TopologiesWind Turbine Generator (WTG) Topologies

g e n e r a t o r

f u ll p o w e r

P l a n tF e e d e r s

a ct od c

d ct oa c

g e n e ra t o r

p a r t i a l p o w e r

P l a n tF e e d e r s

a ctod c

d ct o

a c

g e n e r a t o r

S l i p p o w e ra s h e a t l o s s

P l a n tF e e d e r s

P F c o n t r o lc a p a c i t o r s

a ct od c

g e n e ra t o r

P l a n tF e e d e r s

P F c o n t r o lc a p a c i t o r s

T y p e 1 T y p e 2

T y p e 3 T y p e 4

Type 1 Type 2 Type 3 Type 4 Vestas NM72 1.65 MW, 50/60 Hz

Vestas V80 1.8 MW, 60Hz

GE 1.5 MW, 50/60 Hz

GE 2.5XL 2.0 MW, 50/60 Hz

Vestas V82 1.65 MW, 50/60Hz

Vestas V47 660 kW, 50/60 Hz

GE 3.6 MW, 50/60 Hz

Clipper 2.5 MW, 50/60 Hz

BONUS (now Siemens) 1.3 MW, 50/60 Hz

Gamesa G80 1.8 MW, 60 Hz

Gamesa G80 2 MW, 50 Hz

Enercon E66 1.8 MW, 50 Hz

BONUS (now Siemens) 2.3 MW, 50 Hz

Suzlon S88 2.1 MW, 50Hz

NORDEX N80 2.5 MW, 50Hz

Enercon E70 2.0 MW, 50 Hz

Mitsubishi MWT100a 1 MW, 60 Hz

Fuhrlaender FL 2.5 MW, 60 Hz

REPower MD70 and MD77 1.5 MW, 50Hz

Siemens, 2.3VS82, 2.3MW, 50/60Hz

Suzlon S66 1.25 MW, 50 Hz

REPower MM70 and MM82 2.0 MW, 50Hz

Kennetech 33-MVS, 400kW, 60Hz

Mitsubishi MWT-92/95 2.4 MW

Reference: K. Clark, 2008 IEEE PES GM– Tutorial on Wind Generation Modeling and Controls – DPWPGWG

Partial List of Different Types of Wind Turbines Partial List of Different Types of Wind Turbines

W

Pad-mounted Transformer Equivalent

Wind Turbine Generator Equivalent

PF Correction

Shunt Capacitors

Collector System

Equivalent

Interconnection Transmission

Line

-Plant-level Reactive Compensation

POI or Connection to the Transmission

System

Station Transformer(s)

WPP Equivalent RepresentationWPP Equivalent Representation

Power Flow Representation of WPP in WECC

• WECC developed and adopted guidelines for WPP representation• Based on single-machine representation• Access to guidelines: www.wecc.biz -> Committees -> MVWG -> WGMG

Major components of WPP Equivalent Representation:

• Wind Turbine Generator (WTG) Equivalent and power factor correction (PFC) caps• Pad-mounted Transformer Equivalent• Collector System Equivalent branch.

W

Pad-mounted Transformer Equivalent #2

WTG Equivalent #2 Type 1

PF CorrectionShunt Capacitors

Collector System Equivalent #2

Interconnection Transmission

Line

POI or Connection to the Transmission

System

Station Transformer(s)

Multiple Turbine RepresentationMultiple 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 #1

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

to be a long/weak line feeder

W

Pad-mounted Transformer Equivalent #3

WTG Equivalent #3 of Type 3 PF=1

Collector System Equivalent #3

21 MW

34 MW

45 MW

Total Output100 MW

Equivalent Collector SystemEquivalent Collector System

• Depends on feeder type (OH/UG) and WPP size

• Zeq and Beq, can be computed from WPP conductor

schedule, if available– For radial feeders with N WTGs and I branches:

– Where ni is the number of WTGs connected upstream of

the i-th branch

– This can be implemented easily on a spreadsheet

21

2

N

nZjXRZ

I

iii

eqeqeq

I

iieq BB

1

Equivalent Collector SystemEquivalent Collector System

• Example with N=18 and I=21:

Equivalent Collector SystemEquivalent Collector System

• Sample project data

11

Some segments Some segments are overheadare overhead

Equivalent Pad-Mounted XfmrsEquivalent Pad-Mounted Xfmrs

• Assume identical ZT are effectively in parallel

– For N identical pad-mounted transformers, each with

impedance ZT , the equivalent impedance ZTeq is:

– For 1.5 MVA to 3 MVA, 600V/34.5kV: ZT = 6% on

transformer MVA base; adjustable (fixed) taps

N

ZjXRZ T

TeqTeqTeq on pad-mounted transformer MVA base

on N × pad-mounted transformer MVA base TTeq ZZ OR

Reactive Power LimitsReactive Power Limits

• Type 1 and Type 2 WTGs (induction machines)– At full output and nominal voltage, PF ~ 0.9 under-

excited => Qmin = Qmax = Qgen = -½ Prated

– MSCs at WTG terminals maintain PF near unity at nominal voltage => Qcap = ½ Prated

– Example:

~100 MW WPP, Type 1 WTG• Pgen = Prated = 100 MW

• Qmin = Qmax = Qgen = -50 Mvar

• Qcap = 50 Mvar

Reactive Power LimitsReactive Power Limits

• Type 3 and Type 4 WTGs– Line-side converter allows for PF adjustment at WTG

terminals; MSCs at WTG terminals are not needed

– If WTG PF is fixed, Qmin = Qmax = Pgen × tan(cos-1(PF))

– If WTG PF range is used for steady-state voltage control, set Qmin and Qmax according to PF range and Pgen

• WTG PF adjusted by plant-level controller. Patents may apply.

– Example:

~

100 MW WPP, Type 3,+/-0.95 reactive range, controlling POI voltage

• Pgen = Prated = 100 MW

• Qmin = -33 Mvar; Qmax = 33 Mvar

• Qgen depends on POI voltagePOI

Dynamic RepresentationDynamic Representation

Power System Dynamic Time ScalesPower System Dynamic Time Scales

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

• Objective of the model? (fault transient or long term dynamic, mechanical or electrical characteristics, power system transient or power quality of the wind power plant).

• Major components (wind turbine type 1, 2, 3, 4, include aerodynamic or use simplified one, positive sequence or 3 phase representation, use complete generator and power electronics or simplified power conversion, include system protection?).

• For each component block, the equations governing the function of the block can be derived (assumptions may be made to simplify power converter, aerodynamic, saturation level, nonlinear circuits).

• Control algorithm will be formulated according to the wind turbine system to be modeled (WTG type 1 is different from WTG type 4 etc, different manufacturers may have unique algorithms).

• Choose the method of calculation and/or the software to be used (PSLF, PSSE for positive sequence representation, PSCAD, PSIM, EMTP if detail of the power electronics switching to be emphasized, MATLAB/Simulink, Mathcad may be considered for different aspects of simulation).

Example of Wind Turbine ModelExample of Wind Turbine Model

WECC Generic Models

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

– Type 3 model formally approved for use in WECC; others pending

• 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

WECC Generic Models

generator

Slip poweras heat loss

PlantFeeders

PF controlcapacitor s

actodc

generator

PlantFeeders

PF controlcapacitor s

Type 1 WTG Type 2 WTG

WECC Generic Models

generator

partia l power

PlantFeeders

actodc

dctoac

genera tor

full power

PlantFeeders

actodc

dctoac

Type 3 WTG Type 4 WTG

• 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.

Method of WTG Model ValidationMethod of WTG Model ValidationComparison against field test measurementComparison against field test measurement

Example of Dynamic ModelExample of Dynamic ModelSimulation versus Field Data (Type 3)Simulation versus Field Data (Type 3)

W

Pad-mounted Transformer Equivalent

91% WTGs stays “on” after the fault.

Collector System

Equivalent

Interconnection Transmission

LinePOI or Connection to

the Transmission System

Station Transformer(s)

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

Two Turbine Representation

Interconnection Transmission

LinePOI or Connection to

the Transmission System

Station Transformer(s)

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 4

Time (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

W Wind Turbine Generator Equivalent

InputV and f

A C BSystem Generator

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

Regulated Bus

Example of Dynamic ModelExample of Dynamic ModelSimulation versus Field Data (Type 3)Simulation versus Field Data (Type 3)

• 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.

Method of WTG Model ValidationMethod of WTG Model ValidationComparison against other model (Benchmarking)Comparison against other model (Benchmarking)

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

Terminal Voltage Real Power

Reactive Power Turbine Speed

Parameter SensitivityParameter Sensitivity

The output of the simulation and the measured data can be used to find the total error of the measurement.

Perr = |Pmeas.-Psimulated|

Qerr = |Qmeas.-Qsimulated|

The error and the sensitivity parameter k1 with respect to the error can be computed.

Use the other parameters k1, k2, k3, k4 etc

The parameter sensitivity can be observed from the results.

The trend can be used to drive the changes of the parameters.

Actual Wind Plant

Model with the parameter to be tuned

Input T(k)

+

-

Parameter k

SkT k( ) dT k( )

dk

k

T k( )Sk

T k( )

Parameter Sensitivity - ExampleParameter Sensitivity - Example

Sensitivity of parameter f1 (Sf1) to Perror and Qerror

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.5 1 1.5 2 2.5

f1

Sp

_f1

and

Sq

_f1

Sp_f1

Sq_f1

28/2

Response of P output.

Sensitivity of P output to a range of parameters.Qualitatively similar results for other outputs.Note that a lot of parameters have small and/or correlated influence.Sensitivities obtained as a by-product of running the simulation.

Parameter Sensitivity - ExampleParameter Sensitivity - Example

SummarySummary

Wind power plant model is different from conventional synchronous generator modeling in different aspects:

Different types of generators used (level of capability for reactive compensation, voltage controllability, and LVRT are different)

Wind power plant represents hundreds of generators (i.e. the collective behavior of all turbines is more important than the behavior of individual turbines)

Wind power plant covers a very large area. During faults, each generator may have different operating condition with respect to other generators due to diversity within the wind plant.

The simplification or equivalencing wind power plant may compromise the accuracy of the simulation, however, a complete model requires to represent hundreds of turbines (impractical)

In some cases, components of the system needs to be simplified for many different reasons (NDA, complexity, time constant of interest).