Direct Current (DC) transmission and distribution technologies have undergone a fast development over the past decade. A number of High-Voltage DC (HVDC) transmission lines are being deployed to transfer bulk renewable power in order to reinforce electric power grids with the high penetration of renewables. However, a number of new challenges have been experienced with the HVDC-connected offshore wind power parks, mainly due to the interactions between the HVDC offshore converter and wind turbines. The recent emergence of solid-state transformers also facilitates the development of dc distribution systems. Hybrid ac/dc power grids are thus inevitable in the near future with the increasing use of DC transmission and distribution technologies. The dynamic stability and control of hybrid ac/dc power grids are important for securing a renewable power system.