vestas view on type 3 and 4 generic wind turbine models view on... · vestas view on type 3 and 4...

Vestas view on type 3 and 4 generic wind turbine models

WECC REMTF Wind Turbine Modeling Meeting

Babak Badrzadeh Vestas Technology R&D

[11 July 2011]

Vestas view on type 3 and 4 generic wind turbine models2

Introduction

• Vestas generic wind turbine models for type 3 and type 4 turbines are presented

• Similar models are available for power plant controller but they are not presented here

• The existing model proposals do not provide an accurate representation of Vestas turbines performance during LVRT events

• Different vendors have different LVRT handling philosophy which makes it difficult to achieve a unified model across the industry


Model proposal comparison (1)

ExistingWECCModel

Separate models for type 3 and 4 turbines Static generator model LVRT is handled by low voltage active power and high voltage reactive power

management blocks Extensive use of flags but without any state machine

ProposedIEC/WECC

Model

VestasPerformance

Model

Common structure for type 3 and 4 turbines Static generator model LVRT is handled by current limitation and active-reactive power priority blocks Extensive use of flags but without any state machine

Common structure for type 3 and 4 turbines Dynamic generator model during fault conditions LVRT is handled by the LVRT logic which includes state machines, current

limitation, and dynamic generator blocks Simplified version of the actual state machines is implemented



ExistingWECCModel

For many vendors the model does not produce reactive power performance during LVRT conditions with sufficient accuracy

Do not include drive train torsional damping Do not include active power reference reduction for long voltage dips Do not include a model of dc protection circuit, i.e. chopper or crowbar

ProposedIEC/WECC

Model

VestasPerformance

Model

Produces reactive power performance during LVRT conditions with higher accuracy compared to the existing generic models

Includes drive train damping for type 4 turbines (presumably for type 3 turbines as well)

Do not include active power reference reduction for long voltage dips Includes a model of dc protection circuit

Produces reactive power performance of Vestas turbines during LVRT conditions with sufficient accuracy

Includes drive train torsional damping for type 3 turbines Includes Vestas Defensive Pitch strategy for long voltage dips Do not include a model of dc protection circuit



ExistingWECCModel

Model parameterization is required for turbines other than the default library models

Representation of some of the plant level controllers

ProposedIEC/WECC

Model

VestasPerformance

Model

Model parameterization is required due to several aggregations/transformation applied to the model

Plat level controllers are excluded

Model parameterization is not required for Vestas turbines Plant level controllers are excluded


Vestas power simulation models

• The Process of developing Power Simulation Models• It is used on all components in the Wind Power Plant

FunctionalDescription

Model usage(requirements)

ImplementationDescription

Detailed ModelPSCAD

Model Implementation& documentation(PSSE/PF/PSLF..)

Model designdescription

Measurements

PSCADBlack Box

TSOC

ustomer

PSCADBlack Box


Vestas performance model structure

Aero-dynamic

Mecha-nical

Mech.gen. Elec.

gen.

Current injection+ aggr.

Transformer +

grid

Pitch

PQLimits

Genera-tor ctrl.

Protec-tion

Measurement SW/HW

Windspeed

LSS speed

Gen. speed

Gen. speed

P-airgap

PmechTaero

P* PQ ref

I, Pelec, Qelec

Us, f

P, Q

Us, f

FB2 FB4

Trip

S5

LVRTlogic

FB1

S7

FB3 FB5

Pitchangle

M1

L2L1

Ir

Measurement

Protection

Generator control

PQ-chart

Grid interface

Legend:

Drive train*

LVRT logic

Direct feedthroughPPC

PPC


Factors determining turbine performance during an LVRT event

• A logic deciding switch over from power control mode to current control mode

• Resetting filters and integrator part of PI controllers

• Maintaining turbine operating point within the PQ-chart at any given point

• Modifying the rotor current d- and q-axis reference values (limiting currents as function of voltage)

• Active power reference reduction state machine for long voltage dips

• Dynamic generator state machine (for type 3 turbines) representing electrical dynamics during uncontrolled state (blocked converter operation) and during fault recovery (saturated rotor voltage operation)

• Under/over voltage and frequency protection

LVRT

Logics

Us

Pset

Irq*

Ird*

Sago}L2{FB2

SDFIG


State machines

DFIG dynamic generator state machine

BCONO NO SRVOUcompare < UBCO t - t0,BCO > tBCO Ucompare > USRVO

SDFIG=0 SDFIG=1 SDFIG=2 SDFIG=3

t - t0,BCO > ttimeout

t - t0,SRVO > tSRVO

State=1Normal

Operation

State=2Long dip

State=3Ramp back

Longdip=1 Longdip=0

PWT = Pref

Defensive pitch strategy


Vestas view on modeling dc protection circuits

• Vestas applies dynamic braking chopper to its type 3 and type 4 turbines

• Generally dynamics associated with the grid-side converter are one order of magnitude faster than those of the power controller

• Results of a recent model certification on a performance model of a Vestas full-scale turbine reveals negligible impact from the chopper during LVRT events

• Most dc protection circuits are activated based on sensing abnormal rotor currents

• Generic models cannot provide a precise estimation of the rotor current due to the neglect of rotor current controller

• Other factors determining precise behaviour of the system during an LVRT event includes transformer saturation, but these factors are not generally required for a generic model


Vestas view on asymmetrical fault handling representation

• Most turbines sold worldwide are not required to have the asymmetrical fault handling feature

• With type 4 turbines this feature can be implemented more straightforward

• Correct representation of negative sequence components in a positive sequence program is cumbersome and not well proven in industry

• EMT type programs provide a much better basis for investigation of asymmetrical phenomena

• Asymmetrical phenomena involves additional factors such as system grounding and a more detailed representation of the transformer

• Sufficient representation of the converter control for these types of studies is beyond the intent of generic models


Vestas view on modeling Phase locked loop (PLL)

• Positive sequence PLLs are often used

• This can be readily represented with the built-in PLL blocks or similar functionalities provided in positive sequence simulation tools

• Generally dynamics associated with the PLL are one order of magnitude faster than those of the power controller

• The action of PLL during fault conditions is accounted for by modifying the current reference values

• For too low a voltage dip the PLL is momentarily blocked

• Negative sequence PLLs are only used for turbines designed with asymmetrical fault handling feature


Vestas view on drive train torsional damping model

• Damp generator speed oscillations near resonance frequency of drive train

• Injecting power into the grid

• When the turbine runs in current control mode, the torsional damping controller is disabled

• Drive train damping has some impact on the performance of the type 3 turbine model

• Results of a model certification has shown that for type 4 turbines the drive train damping can be neglected

• The proposed IEC/WECC model for type 4 turbines includes a model of drive train damping but simulation results provided by the working group do not show an appreciable impact


Vestas view on model parameterization

• Exiting WECC models, especially type 3, do not provide an accurate representation of Vestas turbines behaviour during LVRT events

• Results obtained from a preliminary study using trajectory sensitivity analysis do not show a good match with the expected turbine performance:

• Parameters of pitch system can be estimated with reasonable accuracy

• But the behaviour of electrical system during LVRT events cannot be parameterized with sufficient accuracy

• Other model parameterization approaches are being investigated


Conclusions

• Full model documentation and detailed transfer function block diagram representation of all Vestas turbine types are available

• A common model structure applies regardless of the nominal voltage, frequency, and power, and converter control technology

• Differentiators between Vestas performance model and other generic models are highlighted

• In particular, Vestas LVRT handling philosophy differs from many other vendors

• Several add-on features discussed recently are not deemed necessary

• There is a need to distinguish between transient stability models used for model certification and those used for bulk transmission system studies

• The level of details provided to the user must be consistent with the capability and bandwidth of simulation tools adopted for bulk transmission system studies

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