10089_001.pdf - Load set calculation - ECN

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Load set calculation DOWEC 6MW H. Efdé Plots in Appendix I show the behaviour of several towers. 5.4 Turbine control. Three alternative controls are modelled (ref. [11]) and calculated, a High Tip Speed (HTS), Low Tip Speed (LTS) and a Peak Shave (PS) control. The HTS turbine runs with a nominal speed of 12.58 rpm at Vr=11.7 m/s. The LTS turbine runs with 10.36 rpm at Vr=12.3 m/s. The first eigenfrequency of the tower of the HTS control turbine is increased from 0.242 to 0.257 Hz. This will prevent undesired excitations due to the higher nominal speed. The PS control does not change the rpm, but limits the maximum axial force on the hub in this case by opening the blade pitch 2 degrees at Vr. The design of the PS control is based on ref. [15]. The results of the load case calculations can be found on CD C45.04/01.03/03. The extreme and fatigue tables can be found in Appendix F as well. 5.4.1 Cost of energy. For the cost of energy of the HTS and LTS control the average gearbox torque and the annual production is calculated. The average gearbox torque is determined by calculating the average torque of the generator power curve from the Phatas input file “DowecHTS.inp” and “DowecLTS.inp”. Phatas IV is used to create a PV curve of the HTS and LTS control. Consequently with the Phatas post processing program “Eprod” the annual production is calculated. The results are presented in the table below. Table 15: HTS and LTS control, cost of energy. parameter baseline High Tip Speed control relative turbine costs Low Tip Speed control relative turbine costs Blade kNm % % % % Myb[1]-p[01] 18006.00 2.15 0.03 -16.28 -0.24 1Hz-Mxb[2]-p[01] 6740.51 0.72 0.01 -8.45 -0.13 gearbox Mxn mean 30400.28 -5.34 -0.20 3.45 0.13 tower Myt[01] -281560.00 4.94 0.24 -17.98 -0.86 1Hz-Myt[02] 6372.64 4.86 0.16 -9.81 -0.31 total 0.24 total -1.42 annual production baseline HTS change (%) LTS change (%) Gwh 25.4014 25.5353 0.53 24.656 -2.93 HTS control, change in cost of energy (%) - 0.29 LTS control, change in cost of energy (%) 1.47 R45.04/01.03/03 Stentec, 3-1-03 page 18
Load set calculation DOWEC 6MW H. Efdé For the PS control the generator torque table is not changed. Therefore only the blade- and tower parameters and the annual production is taken into account for the calculation of the cost of energy. The results are presented in the table below. Table 16, PS control, cost of energy. parameter baseline Peak Shave control relative turbine costs Blade kNm % % Myb[1]-p[01] 18006 -4.69 -0.07 1Hz-Mxb[2]-p[01] 6740.51 -0.48 -0.01 Tower Myt[01] -281560 -0.18 -0.01 1Hz-Myt[02] 6372.64 -0.20 -0.01 total -0.09 annual production baseline PS change (%) Gwh 25.4014 25.0053 -1.56 PS control, change in cost of energy (%) 1.44 It was expected that the PS control would give greater benefits. Analysis of the load cases and the results show that the axial force (Fxn) is only reduced with 6.10% at loadcase 12PS, compared to the baseline loadcase 12. When running a simple test loadcase with a linear changing wind from 4 to 25 m/s, the Fxn at Vr is even higher than that of the base line as can be seen in Appendix J. It must be concluded that the present peak shave control for the 6MW DOWEC does not work properly. It must be revised and tested prior to drawing conclusions. R45.04/01.03/03 Stentec, 3-1-03 page 19
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