Interaction energy-based power coupling oscillation analysis and suppression of grid-forming converter connected system

The power coupling effect of the grid-forming converter will cause instability oscillation when it connects to lowvoltage short-distance transmission lines. To solve this problem, this paper presents an energy interaction analysis method for oscillation mechanism exploration and damping control of the grid-forming converter. Firstly, the dynamic energy model of a grid-forming converter-connected system is constructed considering power coupling. Then, the energy interaction paths among power control loops are quantitatively explored, the critical interaction paths affecting the system stability are screened, and the grid-connected stability boundary of the grid-forming converter is explicitly described. On this basis, an energy feedback branch is constructed in the critical interaction path to compensate for the negative damping effect caused by power coupling. Its influence on the converter's basic response characteristics is also verified. Finally, A semi-physical simulation platform is built in RT-LAB for experimental verification. The results show that when the line conductance of the transmission line is greater than the steady-state equivalent internal conductance of the converter, the power coupling produces negative dissipation and causes the oscillation divergence. The proposed active damping control method can effectively suppress oscillation while guaranteeing the basic response characteristics. (c) 2017 Elsevier Inc. All rights reserved.