<p>Power generation with the doubly fed induction generator with direct-current link (DFIG-DC) system using tidal speed is indeed highly cost-effective, especially when combined with HVDC transmission. In this work, the proposed DFIG-DC generation system leverages several economic advantages, making it ideal for large-scale offshore tidal energy projects. Nevertheless, harmonic distortion poses a significant challenge in DC-link-based DFIG energy conversion systems, adversely affecting power quality. The studied system comprises a marine current turbine driving a DFIG-DC energy conversion system. In this configuration, a bridge rectifier ensures the connection between the stator windings and the DC bus, while a PWM power converter is inserted between the DC bus and the rotor windings. The control of the DFIG is achieved using field-oriented control (FOC). This paper presents an efficient DC voltage and stator frequency control scheme with harmonic current suppression (HCS) for DFIG-DC system in marine current turbine (MCT) applications. A key contribution is the implementation of a super-twisting sliding mode control (STSMC) algorithm. This method aims to suppress harmonic currents by injecting calculated reference harmonic currents alongside the fundamental d- and q-axis rotor reference currents, thereby enhancing stator current quality. Finally, the performances of the DFIG-DC energy conversion system are shown through digital simulation and experimental results. Additionally, simulation results from <i>MATLAB/Simulink</i> confirm the effectiveness of the STSMC algorithm, which reduces total harmonic distortion (THD) to 5.81%, compared to published approaches. These results give high dynamic performances of the DC voltage regulation and the reduction capability of the harmonics.</p>