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
Vestas view on type 3 and 4 generic wind turbine models3
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
Vestas view on type 3 and 4 generic wind turbine models4
Model proposal comparison (2)
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
Vestas view on type 3 and 4 generic wind turbine models5
Model proposal comparison (3)
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 view on type 3 and 4 generic wind turbine models6
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 view on type 3 and 4 generic wind turbine models7
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
Vestas view on type 3 and 4 generic wind turbine models8
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
Vestas view on type 3 and 4 generic wind turbine models9
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 type 3 and 4 generic wind turbine models10
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 type 3 and 4 generic wind turbine models11
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 type 3 and 4 generic wind turbine models12
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 type 3 and 4 generic wind turbine models13
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 type 3 and 4 generic wind turbine models14
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
Vestas view on type 3 and 4 generic wind turbine models15
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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