Renewable Energy: New transmission concept for wind turbines from the Technical University Munich (TUM).
Wind turbines have a problem: Depending on the wind’s force, the rotational speed of the turbine and thus of the generator changes. However, alternating current must be fed into the grid with precisely 50 (or 60) hertz. Typically the generated alternating current is first rectified and then transformed back to alternating current of the required frequency. Scientists at the Technische Universitaet Muenchen have now developed an active transmission that makes this double transformation superfluous.
Renewable energ – Wind turbine
Picture: Wind Turbine (source: Siemens)
Most large wind turbines currently operate at variable speeds. When the wind is strong, the rotor turns fast; when it slows down, the rotor speed drops. Typically rotors complete 12 to 16 revolutions per minute. The generator is connected to the rotor via a gearbox. Here too, the speed of rotation varies with the speed of the wind.
Yet, a wind turbine may only feed alternating current with exactly the frequency of the electric grid. That is why the alternating current from generators is today transformed into direct current by way of giant rectifiers. In a second step the direct current is then transformed back into alternating current of the right frequency. This twofold conversion takes a loss of close to 5 percent.
In their research, scientists from the Chair of Machine Elements at the TU Muenchen took a closer look at the gears and generator system. To attain the grid frequency of 50 hertz, a generator with the usual two poles pairs must operate at a synchronous speed of exactly 1500 revolutions per minute. To fulfill this requirement in spite of the variable input rotational speed, the researchers developed a novel active torque-vectoring gear analogous to a controlled differential in motor vehicles.