Standard Wind TurbineStandard Wind Turbine--Generator ModelsGenerator ModelsWind Generator Modeling GroupWind Generator Modeling GroupWestern Electricity Coordinating CouncilWestern Electricity Coordinating CouncilIEEE PES 2006 IEEE PES 2006 Montreal, QuebecMontreal, Quebec

Western Electricity Coordinating Council

It is time for a change

Wind generation capacity no longer “invisible”60 GW worldwide, 40 GW in Europe, >9 GW in the US, >4 GW in the WECC footprintSome regions experiencing high saturation levelsSignificant expansion expected in the near future

Adequate simulation models are indispensableEvaluate impact of adding new generatorsPerform planning studies to maintain system reliability at the local and regional level

The Status Quo is not acceptableOne-of-a-kind, proprietary models unnecessarily difficult to refine, validate, and maintain

Yet another A different modeling effort

WECC Wind Generator Modeling Group (MVWG)Convened by Modeling & Validation Work Group (MVWG) in 2005WGMG Members:

Abraham Ellis PNM, WECC (chair)Graeme Bathurst TNEI ServicesJohn Dunlop AWEAYuriy Kazachkov Siemens PTI (PSS/E)John Kehler AESO, WECCEduard Muljadi NRELWilliam Price GE Energy (PSLF)Craig Quist PacifiCorp, WECCJoseph Seabrook Puget Sound, WECCPaul Smith ESB GridRobert Wilson WAPA, WECCRobert Zavadill EnerNex, UWIG

Mission statement

Invest best efforts to accomplish the following:Develop a small set of generic (non-vendor specific), non-proprietary, positive-sequence power flow and dynamic models suitable for representation of all commercial, utility-scale WTG technologies in large scale simulations

The models should be suitable for typical transmission planning and system impact studies

Develop a set of best practices to represent wind plants using generic models as basic building blocks

Coordinate directly with wind manufacturers and other stakeholder groups outside WECC

Proposed standard models

Four basic topologies based on grid interfaceType 1 – conventional induction generatorType 2 – wound rotor induction generator with variable rotor resistanceType 3 – doubly-fed induction generatorType 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

PF controlcapacitor s

Type 1 Type 2 Type 3 Type 4

Technical issuesComplexity vs. completeness

Need the right tool for the job!Wind plant “equivalencing” (e.g., single-generator or several-generator reduced equivalent) necessary and sufficient for both power flow and dynamic simulations

Grid vs. wind disturbancesStandard models are intended for studying the effects of grid disturbances, not wind disturbances

For a typical wind plant, constant wind power during transient events (0 to 20-second time frame) is not a bad assumptionOther tools that account for geographical diversity should be used to study the effect of wind variability in operations planning

Model vs. realityValidation is required--will be challenging!

Wind plant “equivalencing”Individual WTGs and turbine-level reactive compensation (if any)

Collector system with several overhead and underground

feeders underground)

Station transformer & plant-level reactive

compensation (if any)

Power Grid

POI

“Single-generator” equivalent Planning studies typically assume rated MW outputReactive consumption/capability at the POI can be estimated, but should be field-verifiedEquivalent feeder impedance can be derived from design data

Equivalent generator with appropriate VAR range, depending on Pgen (*)

Main station Xfm

Equivalent feeder impedance and shunt

admittance

Equivalent pad-mountedtransformer

Equivalent low-voltage shunt compensation, if any

P.O.I.

Explicit plant-level shunt compensation, if any

System

Wind plant “equivalencing”

NOTE: In some cases, it may be desirable to define a “several-generator equivalent” model

Testing existing models

PurposeCompare performance of a large number of existing custom models for specific disturbance conditionsDetermine whether “category models” would sufficiently capture dynamic behavior of commercial turbines

Test System

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 equivalent Re, Xe, Be

0.6/34.4kV equivalent GSU transformer Rte, Xte

34.4/230 kV station transformerRt, Xt.

Station-level shunt compensation

Turbine-level shunt compensation

2 1 3

4

5

Test scenarios

Scenario System SCR(pre/post fault)

Faultlocation

Clearingtime

(cycles) Output levels

1a 10 / 5 at node 2 9 100% output, rated wind sp.1b 10 / 5 at node 2 9 50% of rated output (50 MW)1c 10 / 5 at node 2 9 100% output, 125% wind sp.2 20 / 10 at node 2 9 100% output, rated wind sp.3 10 / 5 at node 2 5 100% output, rated wind sp.4 20 / 10 at node 2 5 100% output, rated wind sp.5 10 / 5 mid line 1 9 100% output, rated wind sp.6 20 / 10 mid line 1 9 100% output, rated wind sp.7 10 / 5 mid line 1 5 100% output, rated wind sp.8 20 / 10 mid line 1 5 100% output, rated wind sp.

Models tested

Type Make/Model

1 MPS MWT1000A1 Bonus 1.3/2.3 MW1 Vestas V82/722 Vestas V80/472 Suzlon 2.0 MW *3 GE 1.5

Type Make/Model

3 Gamesa G80/903 Vestas V904 Enercon E704 Clipper 2.5 MW4 Bonus 2.3 MW Mark II4 GE 2.x Series **

(*) PSSE only (**) PSLF Only

For the same WTG, model response is very similar in different platforms, even though implementation and level of detail differ

Supports case for a standard model for each generic type of wind turbine generator

Some existing models need improvementTechnical analysis continuesManufacturers willing to cooperate

Some required confidentiality arrangements

Some lessons learned

Type 3 standard model*

Generator/Converter

Model

ConverterControlModel

Ip (P)Command

Pitch ControlModel

PowerOrder

Vreg bus Vterm

Eq (Q)Command

Pgen , Qgen

WindTurbineModel

BladePitch

ShaftSpeedSpeed

Order

Pgen , Qgen

Pgen

Structure and level of user input similar to standard generator models

No special EPCL / IPLAN routinesInitialize directly from power flowSeparate protection model

* Work in progress!

Type 3 standard model*

Vterm

FromConverterControl

Vterm /θ

IYinj

T

Isorc

-1Xeq

ω os

δKpllωoT-1

VY

VX

IPcmdIP1

1+ 0.02s

11+ 0.02s

s

Pllmax

Notes: Vterm and I sorc are complex values on network reference frame.

2. In steady-state, VY = 0, VX = Vterm, and δ = θ .

+

+

jXeq

EqEq cmd

IXinj

1.

PllmaxPllmin

Pllmin

Kipll

Generator / Converter Model

V/Q control of gen. internal EqP control of converter IpPhase-locked loop –not instantaneous

* Work in progress!

Type 3 standard model*

Vterm

Ip cmdTo

Generator /Converter

Model

XPord1

1+ sTpc

Pmax & dPmax/dt

Anti-windupon

Power Limits

Kptrq+ Kitrq / s

(shaft speed)

ωerr

To PitchControlModel

11 + Tsps

ωref

f ( Pgen ) Σ

+Pgen

ω

Pmin & -dPmax/dtTo PitchControlModel

.

.

Ipmax

Vreg

Pgen

Wind Plant Reactive Power Control Emulation

Kiv / s+

Vrfq

11+ sTc

11+ sTr

Qmax

Qmin

1/FnKpv

1+ sTv

Qwv

11+ sTp

-1

Qref

0

varflg1

PFAref tan

x

+

+

Qord

Power FactorRegulator

Qcmd

Qmax

Qmin

++

Qgen

Vref

Vmax

Vterm

Kqv / s

Vterm + XIQmax

Vmin

Eq cmd

ToGenerator /Converter

M odel

Kqi / s

Vterm + XIQmin

vltflg

0

1

Reactive Power Control ModelQ, PFA, or V controlOptional fast Vt control

Active Power (Torque) Control Model

* Work in progress!

Type 3 standard model*

θ

BladePitch

ωreff

Pord

+From

ConverterControlM odel

ωerrω

FromTurbineM odel To

TurbineM odel

11+ sTp

PImax

cmdθΣ+

+Pitch

Control

Kpp + Kip / s

Anti-windup onPitch Limits

PitchCompensation

Kpc+ Kic / s

Anti-windup onPitch Limits

+

Σ

Σ

+

1

PImin

rate limit (PIrate) Pitch Control Model

Wind Turbine Model

* Work in progress!

SimplifiedAerodynamic

M odel

ConstantWind Speed

θ

BladePitch ΔP = Kaero ( θ - θo )

Pmech = Po - ΔP

Pmechω

Σ 1s

12H+

Pgen

:Tacc

ToPitch Control

M odeland

ConverterControlM odel

FromGenerator

M odel

FromPitch Control

M odel

D

Turbine Aerodynamic Model

Detailed aerodynamics in most WTG modelsThe mechanical power (Pmech) applied to the generator is a function of the Power Coefficient (Cp)

Pmech = Pmech = ½½ ×× (air density) (air density) ×× (swept area) (swept area) ×× Cp Cp ×× (Vw)(Vw)33

Cp is a function of blade pitch and tip-speed ratioDuring a large electrical disturbance, blade pitch and tip speed ratio vary, thus Cp and Pmech will also varyCp is modeled using a look-up table or Cp matrix specific to each WTG (usually considered confidential, proprietary information)

Aerodynamic Model Simplification

Assume that during grid disturbances:Wind speed change is negligibleShaft speed change has negligible effect on CpAerodynamic model: Pm = f (θ)

For variable speed WTGs (Type 3 and Type 4), investigation of detailed model has shown:

Change of mechanical power (Pm) varies nearly linearly with change in pitch angle (θ) in the range 0<θ<30 degPm varies linearly with respect to wind speed (Vw) from cut-in to rated wind speedθ varies linearly with respect to Vw for wind speeds above rated

Example – GE 1.5 (Type 3)

Simplified aerodynamic model:

Pm = Pm – θ ( θ - θ ) / 100

Initialization:

Pm = Pelec (from power flow)If Pm < Prated, θ = 0If Pm = Prated and Vw > rated wind speed, use Fig. 9 to compute θ

Example – GE 1.5 (Type 3)

Simplified model – Case 1a Simplified model – Case 1b100% output, rated Vw 50% output

Blue = standard model; Red = simplified model

Simplified model – Case 1c Super-simplified – Case 1c100% output, 125% rated Vw Assumes constant Pm (not good!)

Blue = standard model; Red = simplified model

Lessons learned

For Type 3 and 4 WTGs, aerodynamic simplification is possible without significant loss of accuracy

No need for Cp curves, etc.

Model does not perform as well if aerodynamics are ignored (e.g. constant mechanical power)Similar results expected for Type 1 and 2 WTGs

Relationship between ΔPm and Δθ may not be as linear.Simplified model may involve more complicated equations.

Status

Type 3 and 4 standard model currently under development; Types 1 and 2 to follow

Prototyping and testing models in MatLab prior to implementation is PSLF and PSSE

Significant validation effort needed High-order modelsField recordings (turbine and plant-level)

FutureModel “revisions” based on the same fundamentalsNeed continued collaboration among stakeholders--program developers, wind industry, power industry, other