Efficiency comparison of a 5 MW wind turbine PMSG-equipped generating system using various dc-link voltages

Paper i proceeding, 2012

This article presents an efficiency evaluation of a 5 MW wind turbine generating system comprising of a permanent magnet synchronous generator (PMSG) system as well as an IGBTequipped forced-commutated inverter. Three different inverter dc-link voltage levels are used, 11.8, 10 and 8.4 kV. By using these voltage levels the PMSG is utilised in slightly different ways. The lowest voltage level (8.4 kV) is the minimum voltage level that can be used without going into overmodulation. The highest voltage level (11.8 kV) gives the possibility to utilise Maximum Torque Per Ampere (MTPA) control in the whole operating region and 10 kV is inbetween. The higher the voltage that is used, the lower the copper losses in the machine becomes. It is found that the efficiency of the generating system at the rated operating points are 97.6 % and 97 % when the 11.8 kV and 8.4 kV level respectively are used, of which for the 11.8 kV level 1.44 percentage points of the losses are related to the inverter losses and less than 1 percentage points of the losses are related to the machine losses, while for the 8.4 kV level 1.4 percentage points of the losses are related to the inverter losses and 1.6 percentage points belongs to the machine losses. For an average wind speed of 6 m/s, the annual energy efficiencies for the generator are 99.0, 99.0 and 98.8 percent, for the voltage levels 11.8, 10 and 8.4 kV respectively. For the whole drive system these values are 97.4, 97.6 and 97.5. To sum up, from a pure loss point of view, the 10 kV dc-link voltage level is the most energy efficient.