Impedance modeling and stability analysis of the converters in a double-fed induction generator (DFIG)-based system

Abstract

Harmonic stability of double-fed induction generators (DFIGs) now has become a significant topic because of its harmful impact on power quality issues of the system. Since the double pulse width modulation (PWM) converter is one of the main harmonic sources in DFIGs, it may cause harmonic instability with increasing harmonic contents. Thus, the modeling and stability analyses of PWM converters in DFIGs are essential steps to assess the harmonic stability of DFIGs. Aiming at dual PWM converters, which include the grid side converter (GSC) and the rotor side converter (RSC), this paper divides converters into two parts: circuit modules and control modules. Closed-loop input impedance models of each module are then derived by means of transfer functions. Hence, the stability of the system can be readily predicted through Nyquist diagrams. The contributions of parameters to the system's harmonic stability are also identified. Finally, time-domain simulations are conducted in a real-time digital simulation (RTDS) system. Simulation results confirm that the established impedance model can effectively reveal the stability of the DFIG-based system and can give critical conditions for the occurrence of harmonic instability.