Western Electricity Coordinating Council Standard Wind Turbine-Generator Models Wind Generator Modeling Group Western Electricity Coordinating Council IEEE PES 2006 Montreal, Quebec 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 footprint Some regions experiencing high saturation levels Significant expansion expected in the near future Adequate simulation models are indispensable Evaluate impact of adding new generators Perform planning studies to maintain system reliability at the local and regional level The Status Quo is not acceptable One-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 2005 WGMG Members: Abraham Ellis Graeme Bathurst John Dunlop Yuriy Kazachkov John Kehler Eduard Muljadi William Price Craig Quist Joseph Seabrook Paul Smith Robert Wilson Robert Zavadill PNM, WECC (chair) TNEI Services AWEA Siemens PTI (PSS/E) AESO, WECC NREL GE Energy (PSLF) PacifiCorp, WECC Puget Sound, WECC ESB Grid WAPA, WECC 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 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 Type 1 Type 2 Plant Feeders generator Type 3 Pla nt Fee ders gene rator PF control capacitor s Slip power as heat loss Plant Feeders gene rator ac to dc PF control capacitor s Type 4 Plant Feede rs genera tor ac to dc dc to ac partial power ac to dc dc to ac full power Technical issues Complexity 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 disturbances Standard 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 assumption Other tools that account for geographical diversity should be used to study the effect of wind variability in operations planning Model vs. reality Validation is required--will be challenging! Wind plant “equivalencing” Individual WTGs and turbine-level reactive compensation (if any) POI Power Grid Station transformer & plant-level reactive compensation (if any) Collector system with several overhead and underground feeders underground) Wind plant “equivalencing” “Single-generator” equivalent Planning studies typically assume rated MW output Reactive consumption/capability at the POI can be estimated, but should be field-verified Equivalent feeder impedance can be derived from design data Main station Xfm Equivalent feeder impedance and shunt admittance Equivalent generator with appropriate VAR range, depending on Pgen (*) System P.O.I. Explicit plant-level shunt compensation, if any Equivalent pad-mounted transformer NOTE: In some cases, it may be desirable to define a “several-generator equivalent” model Equivalent low-voltage shunt compensation, if any Testing existing models Purpose Compare performance of a large number of existing custom models for specific disturbance conditions Determine whether “category models” would sufficiently capture dynamic behavior of commercial turbines Test System 230 kV Line 1 R1, X1, B1 Infinite Bus 34.4/230 kV station transformer Rt, Xt. 0.6/34.4kV equivalent GSU transformer Rte, Xte 34.5 kV collector system equivalent Re, Xe, Be Ideal Gen Gen 4 1 230 kV Line 2 R2, X2, B2 2 Station-level shunt compensation 3 5 Turbine-level shunt compensation 100 MW equivalent wind turbine generator Test scenarios Clearing time (cycles) Scenario System SCR (pre/post fault) Fault location 1a 10 / 5 9 100% output, rated wind sp. 1b 10 / 5 at node 2 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 9 100% output, rated wind sp. 3 10 / 5 at node 2 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. Output levels Models tested Type Make/Model 1 1 1 2 2 3 MPS MWT1000A Bonus 1.3/2.3 MW Vestas V82/72 Vestas V80/47 Suzlon 2.0 MW * GE 1.5 (*) PSSE only (**) PSLF Only Type Make/Model 3 3 4 4 4 4 Gamesa G80/90 Vestas V90 Enercon E70 Clipper 2.5 MW Bonus 2.3 MW Mark II GE 2.x Series ** Some lessons learned 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 improvement Technical analysis continues Manufacturers willing to cooperate Some required confidentiality arrangements Type 3 standard model* Vreg bus Structure and level of user input similar to standard generator models Vterm Ip (P) Command Converter Control Model Eq (Q) Command Generator/ Converter Model Pgen , Qgen Power Order Speed Order Pitch Control Model Shaft Speed Pgen , Qgen Pgen Blade Pitch No special EPCL / IPLAN routines Initialize directly from power flow Separate protection model Wind Turbine Model * Work in progress! Type 3 standard model* Vterm /θ 1 1+ 0.02s Eq cm d Eq From Converter Control -1 Xeq I Yinj Isorc IPcm d 1 1+ 0.02s IXinj IP T Pllm ax Kipll s Pllm in Vterm VY T-1 Kpll ωo jXeq + Pllm ax + ω o s δ Pllm in VX Notes: 1. Vterm and I sorc are complex values on network reference frame. 2. In steady-state, VY = 0, VX = Vterm , and δ = θ. * Work in progress! Generator / Converter Model V/Q control of gen. internal Eq P control of converter Ip Phase-locked loop – not instantaneous Type 3 standard model* Reactive Power Control Model Wind Plant Reactive Power Control Emulation Vrfq Kiv / s + Vreg 1 1+ sTr 1/Fn Kpv 1+ sTv PFAref Qmax + Qw v + 1 1+ sTc Q, PFA, or V control Optional fast Vt control Qmin tan Qord 1 Pgen Power Factor Regulator Qmax -1 1 1+ sTp Qgen varflg x 0 Qmin Vterm Vmax + Vref Kqi / s Qcmd + ω (shaft speed) Anti-windup on Power Limits Pgen f ( Pgen ) 1 1 + Tsps ωref + Σ ωerr Kptrq+ Kitrq / s Pmax & dPmax/dt X 1 1+ sTpc Pmin & -dPmax/dt To Pitch Control Model To Pitch Control Model Pord Ipmax . . Kqv / s Vterm + XIQmin Vmin Qref Vterm + XIQmax Ip cmd vltflg Eq cmd 1 0 To Generator / Converter M odel Active Power (Torque) Control Model To Generator / Converter Model Vterm * Work in progress! Type 3 standard model* Anti-windup on Pitch Limits From Turbine ω M odel ωerr Σ + Kpp + Kip / s + + PImax 1 1+ sT p + PImin Blade Pitch θ Σ To Turbine M odel K pc+ K ic / s 1 Pitch Compensation From Generator M odel Constant Wind Speed Blade Pitch θ Pitch Control Model Anti-windup on Pitch Limits + Pord θ cm d Σ Pitch Control ωreff From Converter Control M odel rate lim it (PIrate) Wind Turbine Model Pgen Simplified Aerodynamic M odel Δ P = Kaero ( θ - θ o ) Pmech Pmech = Po - Δ P + Σ Tacc : ω 1 2H From Pitch Control M odel D 1 s To Pitch Control M odel and Converter Control M odel * Work in progress! Turbine Aerodynamic Model Detailed aerodynamics in most WTG models The mechanical power (Pmech) applied to the generator is a function of the Power Coefficient (Cp) Pmech = ½ × (air density) × (swept area) × Cp × (Vw)3 Cp is a function of blade pitch and tip-speed ratio During a large electrical disturbance, blade pitch and tip speed ratio vary, thus Cp and Pmech will also vary Cp 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 negligible Shaft speed change has negligible effect on Cp Aerodynamic 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 deg Pm varies linearly with respect to wind speed (Vw) from cut-in to rated wind speed θ varies linearly with respect to Vw for wind speeds above rated Example – GE 1.5 (Type 3) 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 = 0 If Pm = Prated and Vw > rated wind speed, use Fig. 9 to compute θ Simplified model – Case 1a 100% output, rated Vw Simplified model – Case 1b 50% output Blue = standard model; Red = simplified model Simplified model – Case 1c Super-simplified – Case 1c 100% 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 models Field recordings (turbine and plant-level) Future Model “revisions” based on the same fundamentals Need continued collaboration among stakeholders-program developers, wind industry, power industry, other
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