Adaptive Repetitive Control of DFIG-DC System Considering Stator Frequency Variation

Abstract

This paper presents an adaptive repetitive control method for torque ripple suppression of the doubly fed induction generator (DFIG) system connected to a dc grid considering the stator frequency variation. Since the stator of DFIG is connected to the the diode bridge directly, the stator frequency should be controlled additionally. A novel frequency-locked loop (FLL) based on a second-order generalized integrator (SOGI) is proposed for acquiring stator frequency. The stator fundamental voltage is obtained by the adaptive multi-SOGI. Thus, the low-pass filter can be avoided, which can improve the bandwidth of the control loop. Furthermore, the orientation angle can be acquired by the stator fundamental voltage vector directly, which can avoid the parameter dependence on stator and rotor inductances. Since the stator frequency will be controlled to change in a certain range for efficiency optimization, an adaptive repetitive controller (RC) is added to the rotor current control loop for torque ripple suppression considering the stator frequency variation. Based on a mathematical model of the DFIG control system, the transfer function of the frequency control loop and the torque control loop are derived for analyzing the control performance and parameter design. Finally, the proposed control method is validated through the experiment results.