Enhanced direct power control of doubly fed induction generators

This paper presents an enhanced direct power control (DPC) algorithm for doubly fed induction generators (DFIG) capable of reducing the common mode voltage (CMV). Nowadays the DFIG is often used in high power wind energy conversion systems (WECS). A common problem of converter fed induction machines are the bearing damages due to the bearing currents. The source of this problem is the common mode voltage caused by the converter. Instead of a passive solution like EMI filters or isolated bearings, which imply more costs, this paper obtains an active solution by generating special pulse pattern without additional hardware based on the direct power control. This control strategy needs no space vector modulation and further no knowledge of system parameters like stator resistance. Experimental results for a 4kW DFIG system illustrates the effectiveness of the proposed method.