This paper proposes a methodology of integrated generation-transmission planning of power systems, that considers the penetration of renewable generation sources to be shared by two AC independent systems. Additionally, the methodology also deals with the interconnection of independent AC systems by means of HVDC grids. The methodology makes use of differential evolution optimization algorithms to search the optimal solution of the configuration of the HVDC grid. The methodology is tested on a proposed test system that interconnects IEEE-RTS system and the IEEE 39 bus system and two large generation sources, one a wind farm and the other one large hydroelectric source.