Efficiency improvement in wind turbines by increasing speed range using a tandem connection scheme

The paper describes the use of a tandem power electronic configuration in variable speed wind turbines to improve efficiency by allowing an increase in both rotational speed and maximum power sent to the grid. First, the possible increment in power is determined, limiting both current and losses in the machine to their rated values, but allowing an increase in terminal voltage. Next, the increment in captured energy for different wind distributions is assessed. Finally, the required power rating of the converters in the secondary system is estimated, taking into account that in the proposed system they have the extra task of extracting from the generator and sending to the utility the extra generated power.