Abstract: This paper proposes a high-overload modular commutated converter (MCC) to meet the requirement for converters of robust HVDC in high-overload ability and high economy. First, the topology construction and operation principle of MCC are analyzed in detail. It is pointed out that MCC has soft-switching devices, low energy pulsation, and high overload potential. Then the solutions to several key problems of MCC are discussed, such as wide-range regulation of conversion ratio, dynamic inter-module voltage balancing, and dc-fault clearance for overhead-line-based transmission. Furthermore, MCC is characterized in component quantity, volume, efficiency, as well as cost based on an HVDC system of 500kV/2000MW, and comprehensively compared with a normal IGBT-based MMC. Finally, an MCC product of 15kV/60MVA based on IGCT-Plus is developed and verified by various experiment. The proposed MCC can optimize the volume, cost, and power-loss rate for 50%, respectively, on the basis of existing schemes. Hence, MCC has broad application prospect in electricity conversion and transmission.