Modular multilevel converters (MMCs) for dc applications require an internal circulating ac current to balance the charge of the voltage source module capacitors (VSM). While the frequency of this circulating ac current can be freely chosen, in state-of-the-art MMC structures, this frequency is typically limited to 100s of Hz due to the presence of large string inductors and the high number of switching operations, thereby requiring significant ripple power to be filtered by large VSM capacitors. In this thesis, a novel energy transfer mechanism for dc applications is introduced which is unique in that it employs a current source submodule (CSM) to directly control the circulating ac current of the converter, enabling the frequency of the circulating ac currents to be increased by at least two orders of magnitude. This results in a commensurate reduction in VSM capacitor size compared to state-of-the-art MMCs. Based on this current shaping mechanism, several converter structures are proposed to target a wide range of dc applications including applications requiring isolation, high voltage conversion ratios, and bidirectional operational capability. In each of the proposed converter topologies, only a fraction of the VSMs are required to be switched in a given operating cycle enabling a frequency multiplier effect to occur whereby the effective frequency seen by the magnetics of the converter, as well as the VSM capacitors, is much greater than the switching frequency of the individual VSMs. The core ideas of this thesis are validated through experimental work which is performed using a laboratory-scale prototype based on SiC power devices. Peak efficiencies of up to 97.1% were achieved at an effective operating frequency of 50 kHz. The experimental work demonstrates that converters based on this energy transfer mechanism enable substantive converter volume and cost reduction due to a reduction in capacitive and inductive storage requirements.