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PSCAD/EMTDC-Based Modeling and Flicker Estimation for Wind Turbines

PSCAD/EMTDC-Based Modeling and Flicker Estimation for Wind Turbines. C. Carrillo (1) , E. Díaz-Dorado (2) and J. Cidrás carrillo@uvigo.es, ediaz@uvigo.es, jcidras@uvigo.es Department of Electrical Engineering Universidade de Vigo SPAIN

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PSCAD/EMTDC-Based Modeling and Flicker Estimation for Wind Turbines

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  1. PSCAD/EMTDC-Based Modeling and Flicker Estimation for Wind Turbines C. Carrillo(1), E. Díaz-Dorado(2) and J. Cidrás carrillo@uvigo.es, ediaz@uvigo.es, jcidras@uvigo.es Department of Electrical Engineering Universidade de Vigo SPAIN (1) http:// webs.uvigo.es/carrillo, (2) http://webs.uvigo.es/ediaz

  2. PSCAD/EMTDC-Based Modeling and Flicker Estimation for Wind Turbines • Introduction • Flicker and wind energy • Flicker estimation • Measurements • Modeling • Results • Conclusions

  3. 1. Introduction Presence of wind energy in the generation share has been continuously increasing during last years. IN SPAIN: • During 2008, wind energy sharing was 11%. • In 22th/jan/2009, new records of energy generation were reached: 11.074 MWh and 234.059 MWh/day. • Installed capacity at the end of 2007 was 15.131 MW, 30% higher than the previous year. IN OTHER COUNTRIES: • At the end of 2007, wind energy sharing was 21,3% in Denmark and 11.7 % in E.U. • In E.U., installed capacity has grown from 4.753 MW in 1997 to 56.535 MW in 2007.

  4. volt 38 39 40 time in s 1. Introduction Technical requirements (grid codes) increase its level of exigencies as a consequence of wind energy growing. One aspect to be taken into account is the impact of wind energy in POWER QUALITY. Emission limit • Flicker • Harmonics • Voltage sag ride through Immunity level 100 Nominal voltage (90%) RMS Voltage en % Minimum voltage Sag duration 0 0 time en s 0,8

  5. 7 6 wind speed in m/s 5 wind speed 0 100 200 300 400 500 600 -1 0 1 100 10 10 10 power in kW 50 power 0 100 200 300 400 500 600 -1 0 1 10 10 10 time in s frequency in Hz 2. Flicker and wind energy • Random nature of wind  Random power Power delivered by wind turbines has variations than can provoke flicker due to: • Periodic fluctuations (shadow tower, wind shear, tower oscillations,…)

  6. 2. Flicker and wind energy Grid codes take into account take into account the possibility of flicker emissions from wind plants. So, certain technical requirements are imposed: IN SPAIN: Royal Decree 661/2007: REAL DECRETO 661/2007 installed capacity will be less than a 5% of the short circuit power in the point of connection to the transmission network. Standard organisations also consider this problem. There are specifics standards regarding to flicker and wind energy. IEC: IEC 61400-21 Wind turbines – Part 21: Measurement and assessment of power quality characteristics of grid connected wind turbines (In Spain: UNE-EN 61400-21)

  7. 3. Flicker estimation IEC 61400-21 proposes a method to estimate flicker emission of wind farms. Flicker estimation is done by mean of simulation where current measurements from a wind turbine are injected in a virtual network. virtual network measurements Lfic Rfic flickermeter voltage u0(t) im(t) ufict(t) ufict(t) Pst im(t) simulation flickermeter current measurements simulated voltage flicker

  8. 3. Flicker estimation Flicker estimation is done by using the called “flicker coefficient” c calculated for each wind turbine. • c: is the flicker coefficient • va: is the mean wind speed • Ψk: is the network impedance angle • Pst: is the flicker level emitted by one windturbine • Sk: is the network short-circuit power • Sn: is the nominal apparent power of the windturbine From flicker coefficients, the total flicker Pst,Σemitted for a wind farm is estimated. • Pst,Σ: is the whole flicker level • ci: is the flicker coefficient for windturbine “i” • Sn,i: is the nominal apparent power of the windturbine “i” • N: is the number of windturbines

  9. 4. Measurements Sotavento Wind Park Data for simulation have been obtained from the measurements done in the Sotavento Experimental Wind Park (www.sotaventogalicia.com) placed in the Northwest of Spain (Galicia). Google Earth

  10. 4. Measurements Sotavento Wind Park The Sotavento Experimental Wind Park has installed 24 wind turbines with a total power of 17,56 MW and an estimated annual energy production of 38.500 MWh.

  11. Wind Meter GEN. meter 4. Measurements Long term measurements • Measurements has been done with a long term recorder. Measured variables are: • Voltage (instantaneous and RMS) • Current (instantaneous and RMS) • Power (instantaneous, active and reactive) • Wind Speed (instantaneous) power in kW wind speed in m/s time in s

  12. 4. Measurements Power Oscillations Mean spectrum of Wind Speed and Power have been analyzed to identify power oscillations (tower shadow, wind shear,...) in the power delivered by wind turbines. wind speed spectrum power spectrum frequency in Hz frequency in Hz

  13. 4. Measurements Power Oscillations Main oscillations in power are identified. Most of them are related to the rotation speed of rotor (or low speed shat in drive train). Results for a fixed speed and fixed pitch wind turbine frequency 1p: is related to rotation speed of the rotor -l: low speed of generator -h: high speed of generator

  14. 4. Measurements Power Oscillations Main oscillations in power are identified in different wind turbine topologies installed in the Sotavento Experimental Wind Park. Frequencies 1P and 3P are the most important. Summary of Results

  15. 5. Modeling Wind Turbines • PSCAD have been used for simulation. Elements to be modeled were: • Aerodynamic model, turbine behavior. • Drive train • Generator • Network • Power electronics (AC/AC converter)

  16. 5. Modeling Wind Turbines Wind turbines topologies installed in Sotavento have been modeled. Fixed Speed AG Variable Speed. DFIG AG Variable Speed. Sync. Gen. + AC/AC Converter SG

  17. 5. Modeling Aerodynamic model • To estimate mechanical torque in the generator shaft, the following components have been considered: • Rotor aerodynamic behavior • Oscillating power components Wind Speed Mechanical Torque Total Mechanical Torque Pitch Rotor Speed Oscillating Torque Power Oscillations Calculation Wind Speed

  18. 6. Results Comparison against measurements Measurements are compared with results from simulation. In following graphics a comparison is done between: • Power simulated • Power measured • Estimated Oscillating Power Components Results for a fixed speed and fixed pitch wind turbine power in W P simulated P measured P oscillations TIME SERIES time in s POWER SPECTRUM power in W P simulated P measured P oscillations frequency in Hz

  19. 6. Results Comparison against measurements Results for a fixed speed and variable pitch wind turbine P simulated P measured P oscillations power in W TIME SERIES time in s POWER SPECTRUM power in W P simulated P measured P oscillations frequency in Hz

  20. 6. Results Comparison against measurements Results for a variable speed and variable pitch wind turbine (synch+ AC/AC) power in W P simulated P measured P oscillations TIME SERIES time in s POWER SPECTRUM power in W P simulated P measured P oscillations frequency in Hz

  21. 6. Results Comparison against measurements Results for a variable speed and variable pitch wind turbine (DFIG) power in W P simulated P measured P oscillations TIME SERIES time in s POWER SPECTRUM P simulated P measured P oscillations power in W frequency in Hz

  22. Shorcircuit Power at 132 kV (MVA) Scc Min 4755 Scc Max 5023 Scc 20x 20 x 17.5 MVA 6. Results Flicker estimation • From simulation data a flicker estimation at HV level with different short circuit capacity values have been analyzed: • Scc Min. and Max. are the minimum and maximum values of short circuit power in the wind farm at 132 kV level. • Scc 20x is the short circuit power obtained by multiplying the power of wind farm by 20. Flicker estimations for each of the above situations have been done.

  23. Scc WT (MVA) 6 Scc WT ( º ) 71,56 Mean Wind Speed (m/s) 9,2344 Pst WT Sim. 0,027209 Flicker Coefficient 0,25508 Pst Scc Max 0,00018 Pst Scc Min 0,00017 Pst Scc 20x 0,00249 6. Results Flicker estimation Results for a fixed speed and fixed pitch wind turbine (640 kW) Short circuit values at 132 kV level during Scc simulation Wind Speed during simulation Pst calculated for a single WTG Flicker coefficient (IEC 61400-21) Flicker at short-circuit power Scc Min Flicker at short-circuit power Scc Max Flicker at short-circuit power Scc 20x Pst Scc Max, Pst Min and Pst Scc 20x values have been calculated supposing a wind farm formed for N equal WTG with a total power of 17.5 MW (approx.)

  24. Scc WT (MVA) 6 Scc WT ( º ) 71,56 Mean Wind Speed (m/s) 8,1795 Pst WT Sim. 0,026456 Flicker Coefficient 0,26456 Pst Scc Max 0,00018 Pst Scc Min 0,00017 Pst Scc 20x 0,00247 Scc WT (MVA) (MVA) 13 Scc WT ( º ) 71,56 Mean Wind Speed (m/s) 7 Pst WT Sim. 0,022304 Flicker Coefficient 0,22304 Pst Scc Max 0,00022 Pst Scc Min 0,00021 Pst Scc 20x 0,00307 6. Results Flicker estimation Results for a fixed speed and fixed pitch wind turbine (600 kW) Results for a fixed speed and variable pitch wind turbine (1300 kW)

  25. Scc WT (MVA) (MVA) 13 Scc WT ( º ) 71,56 Mean Wind Speed (m/s) 8,38 Pst WT Sim. 0,012706 Flicker Coefficient 0,25027 Pst Scc Max 0,00018 Pst Scc Min 0,00017 Pst Scc 20x 0,00248 Scc WT (MVA) (MVA) 13 Scc WT (º) 71,56 Mean Wind Speed (m/s) 10,76 Pst WT Sim. 0,022567 Flicker Coefficient 0,39116 Pst Scc Max 0,00030 Pst Scc Min 0,00028 Pst Scc 20x 0,00414 6. Results Flicker estimation Results for a fixed speed and fixed pitch wind turbine (660 kW) Results for a fixed speed and variable pitch wind turbine (750 kW)

  26. Scc WT (MVA) (MVA) 13 Scc WT ( º ) 71,56 Mean Wind Speed (m/s) 10,76 Pst WT Sim. 0,037043 Flicker Coefficient 0,36482 Pst Scc Max 0,00037 Pst Scc Min 0,00035 Pst Scc 20x 0,00511 6. Results Flicker estimation Results for a fixed speed and fixed pitch wind turbine (1320 kW)

  27. Scc WT (MVA) (MVA) 13 Scc WT ( º ) 71,56 Mean Wind Speed (m/s) 10,3526 Pst WT Sim. 0,09 Flicker Coefficient 1,77273 Pst Scc Max 0,00125 Pst Scc Min 0,00119 Pst Scc 20x 0,01755 Scc WT (MVA) (MVA) 13 Scc WT ( º ) 71,56 Mean Wind Speed (m/s) 10,3616 Pst WT Sim. 0,044174 Flicker Coefficient 0,71783 Pst Scc Max 0,00055 Pst Scc Min 0,00052 Pst Scc 20x 0,00774 6. Results Flicker estimation Results for a variable speed and variable pitch wind turbine (DFIG, 660 kW) Results for a variable speed and variable pitch wind turbine (Sync, 800 kW)

  28. 6. Results Flicker estimation The effect of including the power oscillation components is demonstrated in the examples shown bellow. Results for a fixed speed and fixed pitch wind turbine (600kW) Results for a fixed speed and variable pitch wind turbine (1300 kW)

  29. 7. Conclusions • - In this paper, a method to evaluate flicker based in IEC 61400-21 is presented. The current measurement values used in this standard have been replaced for a complete WTG model. • - Oscillating power components(shadow tower, wind shear...) has been included in order to obtain results that are more realistic. • WTG models have been validated by comparing the simulation results with the measured data. • The proposed method allows calculating of flicker emission in single WTG or wind farms at different working conditions.

  30. PSCAD/EMTDC-Based Modeling and Flicker Estimation for Wind Turbines Thank you for your attention ! C. Carrillo(1), E. Díaz-Dorado(2) and J. Cidrás carrillo@uvigo.es, ediaz@uvigo.es, jcidras@uvigo.es Department of Electrical Engineering Universidade de Vigo SPAIN (1) http:// webs.uvigo.es/carrillo, (2) http://webs.uvigo.es/ediaz

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