DC-energy-pool-based multiterminal grids are gaining widespread acceptance under the super- and smart-grid vision. DC-link voltage control via a master voltage-source converter (VSC) is essential to ensure stable and reliable operation of the overall multiterminal system. In such a demanding application, conventional dc-link voltage controllers, however, suffer from stability and performance issues, mainly attributed to the small-signal-based control design approach and the use of a cascaded control structure based on the power-balance framework which yields unmodeled nonlinear dynamics. To overcome these issues, this paper presents a natural-frame variable-structure-based nonlinear control system for the master VSC applied in dc-energy pool multiterminal grids. The proposed controller accounts for the complete nonlinear dynamics of the master VSC without any cascaded control structure and globally stabilizes the nonlinear dynamics via a passivity-based design approach. Analysis and comparative simulation as well as experimental results are presented to show the effectiveness of the proposed controller.