This paper proposes a hierarchical cooperative control scheme to ensure stable operation of islanded dc microgrid (MG) clusters in high renewable energy sources (RES) penetration scenarios. This scheme can be divided into two levels. In the primary level, a cooperative method based on the local bus voltage information is presented, by which the distribution generators (DGs) and the energy storage system (ESS) in each MG can be coordinated together to regulate the local bus voltage within a certain range. In the secondary level, an adaptive droop method for each MG is introduced to control the power flow of the tie-line among the multiple MGs. Moreover, the reference for the operation of the ESS is automatically adjusted to accommodate the changes of DGs' droop characteristics, which are caused by the adaptive droop control. The effectiveness of the hierarchical cooperative control scheme for MG clusters is verified by MATLAB/Simulink simulations.