Power Quality Andrew Kusiak 2139 Seamans Center Iowa City, Iowa 222-127 andrew-kusiak@uiowa.edu Tel: 319-33-93 Fax: 319-33-669 http://www.icaen.uiowa.edu/~ankusiak Outline Power ramps Reactive power Optimization power quality Conclusion Power Ramps Variable winds Different horizons wind farm power time function, e.g.: weeks days hours (of interest at present time) minutes Definition PRR (Power ramp rate): measure of the degree of the power change during a certain time interval Pt ( T) Pt ( ) PRR T [kw/min] Pt ( T ) Pt ( ) PRR 1% [%/min] T NPP t is the current time T is the time interval of the power change NPP (nameplate power) is the power of the wind farm 1
Data Description 133. MW rated power wind farm SCADA collected data is stored at 1-minute intervals (1-minute average data) Model built of 368 data points Tested on 887 data points Data Description Data set Start Time Stamp End Time Stamp Description 1 1/1/6 1: AM 1/31/6 11: PM Total data set; observations 2 1/1/6 1: AM 1/2/6 8: PM Training data set; 368 observations 3 1/2/6 8:1 PM 1/31/6 11: PM Test data set; 887 observations T + 1 Min Power Prediction (1-min Ahead Predictions) Metrics Used in PRR Prediction AE: Absolute error AE y yˆ y is the observed PRR, ŷy is the predicted PRR Units: kw/min or %/min 2
T + 1 min PRR Prediction (1-min Ahead Predictions) Statistics for PRR of Top 1% of Wind Farm Capacity AE kw/min %/min Mean 191.71.1397 Std 183.89.137786 Max 191.31.817832 Min.16 The unit of PRR is kw/min (13. MW rated power) AE = Absolute Error (13.MW rated power) Statistics for PRR of Mid-range 2% of Wind Farm Power Summary AE kw/min %/min Mean 67.627.31 Std 81.19.361 Max 36.387 2.66 The results presented were prepared in a short time for illustrative purposes The results presented can be greatly improved Confidence index is possible to develop Min 8.131.6 AE = Absolute Error (13. MW rated power) 3
P PF S 2 2 2 S P Q P S cos Power Quality S Q P PF: power factor; P: active power measured in W (Watts); S: apparent power measured in volt-amperes (VA); Q: reactive power measured in reactive volt-amperes (Var); : phase angle between current and voltage. Active power (kw) 3 3 2 2 1 1 1 16 31 6 61 76 91 16 121 136 11 166 181 196 211 1 - minute data S Q P Wind speed (m/s) Power Factor Power factor 7 6. 6.. 3. 3 2. 2 1 16 31 6 61 76 91 16 121 136 11 166 181 196 211 1 - minute data 1.2 1.8.6..2 1 16 31 6 61 76 91 16 121 136 11 166 181 196 211 1 - minute data Power quality improvement Power factor is a comprehensive metric to power quality. The controllable variables of wind turbine adjust the generator load, and thus the low power factor could be increased, then the power factor impacts the harmonic distortion and transient overvoltage in the power system. The ideal goal of wind turbine is to set power factor as one or unit power factor; however, power factor is hard to control, and thus it is usually far below one in electricity industry. Metrics for dynamic models N AE() i i MAE N AE yˆ y 1 Std N ( AE( i) MAE) i 1 N 1 ŷ : predicted corresponding parameters; y : observed values of corresponding parameters, and they could be the active power, power factor and rotor speed; N : the number of test data points used to validate the performance of the dynamic MISO models; The small value of the MAE and Std implies a superior prediction performance of the wind turbine models.
Optimization framework Data description Data set Start Time Stamp End Time Stamp Description 1 7/1/8 12: AM 7/31/8 11: PM Total data set; 66 observations 2 7/1/8 12: AM 7/2/8 12: AM Training i data set; 37 observations 3 7/2/8 12:1 AM 7/31/8 11: PM Test data set; 19 observations Low wind speed scenario Optimal vs original active power Wind speed (m/s) 8. 8 7. 7 6. 6.. 1-minute data Activve po ower (kw) 8 7 6 3 2 1 Optimal Power Original Power
Optimal vs original power factor Optimal vs original blade pith angle Power facto or 1 9 8 7 6 3 2 1 Picth ang gle ( ) 6 3 2 1-1 -2-3 Optimal PF Original PF Optimal PA Original PA Optimal vs original generator torque Optimal vs original rotor speed 7 6 18 17 Generator torque 3 2 1 Rotor speed (rpm) 16 1 1 13 12 11 1 Optimal Torque Origina l Torque Optimal rotor speed Original rotor speed 6
High wind speed scenario Optimal vs original power output wind speed (m/s) 11. 11 1. 1 9. 9 8. 8 Active powe er (kw) 1 1 13 12 11 1 9 8 7 6 1-minute data Optimal power Original power Optimal vs original power factor Optimal vs original pitch angle Power fac ctor 1 9 9 8 8 7 Picth angle ( ) 3 2 1-1 -2 Optimal PA Original PA Optimal PF Original PF 7
Optimal vs original generator torque 1 9 Optimal vs original rotor speed 19. 19 Generator r torque 8 7 6 Rotor spe eed (rpm) 18. 18 17. 3 17 Optimal torque Original torque Optimal rotor speed Original rotor speed 8