An LC Oscillation Suppression Method Based on SOGI-FLL for Permanent Magnet Traction System

Under constant power conditions, the DC-link LC oscillation is made worse by the negative damping properties of the permanent magnet traction system (PMTS), endangering urban rail trains' steady and safe operation. In addition, affected by the device aging, the LC resonance frequency point may shift. It poses a new challenge for traditional oscillation suppression. To address this, this paper proposes an enhanced oscillation suppression strategy based on a second-order generalized integrator with a frequency-locked loop (SOGI-FLL). Specifically, the LC resonance frequency of the DC-link is dynamically tracked by the SOGI-FLL, while the virtual impedance is introduced to increase the system damping. Afterward, the modulation voltage is reconstructed to ensure the stability of the traction system. Since the proposed suppression method can be used to adaptively adjust the frequency of harmonic extraction according to the change of LC resonant frequency, the stability of the traction drive system under device aging is enhanced. The simulation results and hardware-in-the-loop (HIL) test results prove the feasibility and correctness of the oscillation suppression strategy.