Resonance characteristic analysis and damping control for LCL-filter-based voltage source converter during bus transfer

This paper investigates a new resonance issue of LCL-filter-based voltage source converters (VSCs). Unlike the traditional resonance issue under normal operating condition, the new potential issue is exposed in the application of automatic bus transfer system (ABTS), due to a temporary change of LCL filter structure during bus transfer. The resonance-induced current and voltage spikes may cause damage or nuisance tripping to sensitive equipment, leading to failure of the automatic transfer and interruption of the continuous process. To solve this problem, the transformation of resonance characteristics during bus transfer is analyzed in this paper. Furthermore, the influence factors to the system stability are obtained, and the stable regions of the factors are derived with Nyquist criterion. Besides, when the system parameters locate within the unstable region, a comprehensive damping scheme with an all-pass filter based multiple notch filter is proposed to solve both resonance issues. With the proposed damping strategy, a smooth bus transfer can be achieved without additional hardware. Finally, the experiments are provided to confirm the stability analysis and validate the effective damping scheme developed in this paper.