Resonance Issues and Damping Techniques for Grid-Connected Inverters With Long Transmission Cable

An infinite source with series inductance is usually employed as a grid emulator in grid-connected distributed generation systems. Thus, high capacitance of a transmission cable (i.e., underground cable) is too significant to be neglected. As a result, the capacitance and inductance may cause system resonance, which, in turn, challenges system stability. This paper takes offshore wind farm as an example to investigate the resonance issues caused by the submarine transmission cable of the grid-connected generation system. Based on the submarine cable model, a series of considerable resonant peaks is found in the open-loop transfer function of the grid-connected system because of the high-order LC configuration. The resonant peaks are sensitive to the system setup, which is clearly investigated. To overcome the resonances, this paper proposes a cascaded notch-filter-based active damping method to guarantee a good system stability and robustness. Furthermore, the proposed controller employs a proportional-resonant component to reduce the steady-state error of the output current. The simulation and experimental results have validated the findings of resonances and the effectiveness of the proposed controller.