Stability Improvement for Multi-inverter System Based on Active Damper with Modified Resonance Detection Method

Due to wide variation of grid impedance and the interactions among the parallel gird-connected inverters, resonance phenomena and stability problems are inevitable. To address the problem, this paper proposes an improved resonance detection method applied to active dampers to improve the stability of parallel grid-connected inverters. Compared with resistive active power filters, the active damper enjoys the benefit of wide frequency range suppression of the specific harmonic and resonance with higher switching frequency and lower power rating. Further, the accuracy of resonant frequency to be compensated is guaranteed by the proposed modified resonance detection method which could estimate the system resonance frequency accurately and is applied to active dampers to suppress the interharmonics and subharmonics effectively. Finally, the simulation results verify the effectiveness and feasibility of the modified detection method.