Control and simulation of doubly fed induction generator for variable speed wind turbine systems based on an integrated Finite Element approach

Transcription

1 Control and simulation of doubly fed induction generator for variable speed wind turbine systems based on an integrated Finite Element approach Qiong zhong Chen*, Michel Defourny #, Olivier Brüls* *Department of Aerospace and Mechanical Engineering (LTAS), University of Liège, Belgium # SAMTECH Headquarters, Liège, Belgium EWEA 2011, Brussels, Belgium

2 Outline Background Control of DFIG Integrated simulation approach Examples & validation Conclusions 1

3 Background Wind turbine concepts Equipped gen. types WT types DFIG WTs FSWTs FCWTs Other Gen. types DFIG SCIG PMSG, SCIG etc. OSIG (Data source: A. Perdala, dynamic models of wind turbines, PhD thesis, 2008) Evolution of WT size: Increased flexibility Increased coupling effects (Figure from EWEA factsheets) 2

4 Background Computer-aided analysis for WT systems Software specialized in a certain field Aerodynamics: AeroDyn etc. Structure: ADAMS/WT etc. Electrics: DIgSILENT etc.? Different systems on different simulation platforms?? No detailed coupling analysis Integrated simulation packages: GH Bladed, Simpack Wind, HAWC2, FAST etc.? Weak coupling (DLLs or co-simulation)?? Numerical stability? Need for integrated optimization tools (Bottasso, 2010) 3

5 Background Samcef for Wind Turbine (S4WT) Nonlinear FE flexible multibody solver: SAMCEF/MECANO One single platform: Aeroelastics, multibody, control, electrodynamics etc. Flexibility in blades, shafts, tower etc. Simulation approaches: Weak & strong coupling An integrated model on S4WT (Courtesy: Samtech) 4

6 Highlights of the paper Improved control strategies of DFIG WTs Grid-synchronization Power optimization Strongly-coupled approach for mechatronic systems [B. & Golinval 2006] Integrated structure-control-generator analysis on S4WT Brüls, O. and Golinval, J. C. The generalized-α method in mechatronic applications. Zeitschrift für angewandte mathematik und mechanik (ZAMM) 86, 10 (2006),

7 Control of DFIG Working process of WT systems Wind turbine Gear box SWr DFIG RSC AC/ DC SWs GSC DC/ AC Transformer SWg Grid A schematic configuration of a DFIG wind turbine Control of DFIG: soft grid connection power optimization Wind power 0 Power Optimization A B C D Wind speed Power Limitation E Turbine output power Power Limitation D, E Power Optimization C B 0 A Rotor speed 6

8 Grid synchronization control Objective: Regulate stator voltage, frequency, phase angle grid before connection Method: Grid-voltage-oriented reference frame Vector control PI Controller designed based on internal model control (IMC) method iqr_ref + _ FF term C qr (s) sli l r dr + _ + V qr + sli l r dr DFIG G r (s) iqr idr_ref + _ FF term C dr (s) sli l r qr sli _ + + V dr + l r qr DFIG G r (s) idr D,q-axis rotor current control loops 7

9 Power control Objective: Follow a pre-defined power-speed characteristics profile speed regulation Method Stator-flux-oriented reference frame Vector control q-axis rotor current active power d-axis rotor current reactive power IMC or pole placement method for design of controllers 8

10 Power control Power control scheme ref + _ controller: C Tω (s) T e_ref controller: C it (s) i qr_ref + _ controller: C vi_qr (s) v qr i qr Qref controller: C iq (s) i dr_ref + _ controller: C vi dr (s) vdr DFIG i dr Decoupled speed and reactive power control of DFIG Controllers: PI or IP regulators Design of controllers PI : IMC method (current loop) IP : pole placement method (speed loop) 9

11 Design of controllers PI controller for q-axis rotor current i-v transfer function G vi_qr I () s V qr qr () s 1 () s X Rr ω 1 s s iqr_ref + _ C vi_qr (s) V qr E qr + G vi_qr (s) iqr PI controller on IMC current control block C s G s X R 1 1 r vi_qr () qr () s ωs s IMC parameter: = ln 9 / t rise For electrical dynamics, the rise time is set to 10ms 10

12 Design of controllers IP controller for speed control Close-loop transfer function () s K/J = s s + K /J s+k /J r i 2 ref () ( p ) i Pole placement method ref + K i /s _ + + T e_ref + _ K p T m 1/(Js) r K p= 2 d ndj 2 K= i ndj Speed control block For over-damped systems: nd = 5.8/t sd For mechanical dynamics, the settling time is set to 1s, DFIG alone 2.5s, with WT system 11

13 Integrated simulation approach Strongly-coupled representation for mechatronic systems y ( q, q, q, ) Mechanism Control system Coupling in a mechatronic system Extended generalized-α solver Mq Φ ( λ Φ) g(q,q, ) L y 0 T a q k p t kφ(q) 0 x f(q,q,q,λ,x,y, t) 0 y h(q,q,q,λ,x,y, t) 0 Coupled 1 st / 2 nd order systems Second order accuracy Unconditional stability More details can be referred to [B. & Golinval 2006] 12

14 Mechatronic Modelling on SAMCEF Considerations for the Mechatronic modelling: Functional system decomposition Modularized, parameterized components E.g. DFIG, PI, PID modules etc. Nodes are introduced for Mechanical DOFs A uniform tangent matrix for State variables Newton iteration Outputs On a general-purpose use User-friendly Reusable 13

15 Examples & validation 2MW DFIG parameters: Base voltage (line-to-line): V base = 690 V; Base power: P base = 2 MW; Grid frequency: f s = 50 Hz; Number of poles: n p = 4; Stator resistance: R s = p.u.; Rotor resistance : R r = p.u.; Stator Leakage inductance: L sl = p.u.; Rotor leakage inductance: L rl = p.u.; Mutual inductance: L m = p.u.. Inertia of the generator rotor: 100kg m 2 WT parameters: Blade length: 41m; Tower height: 75m; Gearbox ratio: 106 Etc. 14

16 Ex. 1:DFIG with defined input torque Simulation situation Synchronization process starts at 0.8 p.u. of the rotating speed Reactive power reference: 0 p.u. Speed (active power) control situation: Reference speed: 1 p.u., time 4sec s 0.9 p.u., 4sec time 6sec 1.1 p.u., time 6sec Input torque: T m 1 p.u., time 8.5sec 0.5time 5.25 p.u., 8.5sec time 9.5sec 0.5 p.u., time 9.5sec 15

17 Results Grid synchronization Synchronization starts Synchronization finishes A-phase grid voltage A-phase stator voltage Grid synchronization process 16

18 Results Power control Speed response i qr i dr Rotor current response Reactive power response 17

19 Ex. 2: DFIG with WT structure model Integration of DFIG with WT structure model on S4WT Simulation situation: Initial WT speed: 1.1rad/s (0.74p.u.) Grid synchronization starts at 0.8p.u. of generator speed Reactive power reference: 0 Active power control according to wind speed: WT models on S4WT wind 8 m/ s, time 8sec 11 m/ s, time 8sec 18

20 Results Grid synchronization Synchronization starts Synchronization finishes A-phase grid voltage A-phase stator voltage Grid synchronization process 19

21 Results Power control Schematic power-speed characteristics Speed response Reactive power Active power Power response 20

22 Results Influence of structural flexibility Blade Rigi. Flex. Young s module (Gpa) Damping (N/m/s) 4.55e e-3 Shaft Rigi. Flex. Bending stiffness (Nm/deg) Bending damping (kg m 2 /s) 0 0 Torsional stiffness (Nm/deg) Generator torque Torsional damping (kg m 2 /s) Other applied elements: Flexible tower Simple gearbox, bedplate elements etc. Speed response 21

23 Conclusions Improved control strategies for DFIG Grid synchronization & power control Solution to the difficulty in the configuration of the controllers coefficients Integrated FE approach with strong coupling instead of weak coupling Unconditional stability, less intricacy Could be less efficient Modular models of the generator/control systems for S4WT package (on a general purpose) Integrated variable-speed DFIG WT system model analysis and validation 22

24 In acknowledgement of DYNAWIND (grant number: ) funded by Wallonia government, Belgium Thank you for your Attention! 23