Common mode voltage minimized direct power control of the grid side connected converter in doubly fed induction generators

Nowadays the doubly fed induction machine (DFIG) is often used as a generator in high power wind energy systems. Advantages in comparison to a synchronous generator are the small size of the converter and the viable alternative to adjust speed over a wide range. Decoupled control of active and reactive power can be realized using a dynamic model of the DFIG. Instead of a classic space vector modulation this paper presents a direct power control. Furthermore, bearing damages can occur specially for this type of machine, because of the use of two converters in the generatorpsilas rotor circuit. Instead of using additional filter-hardware to reduce the common mode voltage, which is the cause for bearing currents, an enhanced direct power control is applied. The results are presented as simulations as well as measurements.