Performance improvement of DPC in DFIGs during unbalanced grid voltage based on extended power theory

Abstract

Doubly fed induction generator (DFIG) control process is more complex in the calculations under voltage unbalance condition because of the power oscillations, and the conventional controllers cannot maintain the system in a stable and smooth condition. In this paper, a flexible method is presented to control the DFIG based on an improved extended power theory on the direct power control platform. The proposed method can simultaneously improve electromagnetic torque oscillations, reduce total harmonic distortion (THD) of stator currents and eliminate active or reactive power oscillations by controller of rotor side converter. The main control system relations based on an analytical process are presented. The improved extended power theory method has made the proposed control independent from decomposition of the positive and negative sequence components which provides ease of the calculation and better performance accuracy. Compared to the conventional extended theory, the proposed method is capable to reduce the torque oscillations, reduction of the stator current THD, and eliminating the powers oscillations of the DFIG. Also, In order to maintain the appropriate dynamic response, a switching table is presented according to the proposed method. The simulation results are clearly confirmed that the proposed method improves the DFIG performance in view of the oscillations under the voltage unbalance conditions.

Keywords

• DFIG
• Unbalanced grid voltage conditions
• Direct power control
• Extended power theory
• Torque oscillation