Modeling and improvement of direct power control of DFIG under unbalanced grid voltage condition

• Operation of a DFIG under unbalanced supply voltage conditions is investigated.
• The modeling is done using oscillating power terms definition.
• The DPC technique is improved by a proper power reference generation.
• Several control targets are indentified and applied to the DFIG.
• Effectiveness and robustness of the proposed method is studied.

This paper presents analysis and control of a doubly-fed induction generator (DFIG)-based wind generation system operating under unbalanced grid voltage condition. The DFIG system is modeled in synchronous positive reference frame. System behavior and operation of both the generator and the grid side converter (GSC) under unbalanced condition is illustrated by definition of oscillating power terms in the synchronous reference frame. This analysis makes it possible to control both the active and reactive power generation by means of direct power control (DPC) technique. It is shown that considering the DFIG model in synchronous reference frame simplifies the power terms extraction. Moreover, alternative DFIG control targets such as reducing unbalanced stator current, torque and power pulsations minimization, are considered. In addition, by the proposed method, the oscillation of the stator output power is compensated by the GSC, to ensure constant power output from the overall DFIG generation system. The validation of results has been performed through simulation results on a 2 MW DFIG wind generation system.