Virtual power line control for interlinking converters on AC, DC and hybrid grid links

Abstract

The increasing integration of renewable energy sources is making power systems evolve, driving the necessity to interconnect different power systems to improve the robustness and operation of grids. Here, the so-called virtual power line (VPL) control for interlinking converters (ICs) is presented, whose purpose is to couple different electric systems analogously to a classical transmission line. The VPL control employs local measurements, and it does not require any communication link to operate. Two VPL control variants are presented: the dual grid-supporting VPL control and the single grid-forming VPL (SGF-VPL) control. Both support the frequency and/or voltage of the interconnected grids, and the latter provides grid-forming capabilities for one of the interconnected systems. The performance of VPL controllers show how the frequency and voltage nadir values are improved by $36\%$ (when comparing low and strong coupling results), while the rate of change of frequency and voltage can be decreased by $49.6\%$, with a $40\%$ faster settling time. Furthermore, it is demonstrated how the SGF-VPL is able to set the grid when other grid-forming units fail, and the flow of power happens naturally through ICs from generation to consumption areas as if all devices were part of the same electric system.