This paper presents a simulation model of the grid connection system for a marine current energy converter deployed in the river Dal (Dal¨alven) at S¨oderfors, Sweden. The implementation of the model is done in MATLAB/Simulink. The experimental station consists of a five-bladed turbine connected to a permanent magnet synchronous generator (PMSG) and a bidirectional back-toback (B2B) converter for the grid connection. The generator side of the electrical system consists of a 2-level voltage source converter (2L-VSC). The generator side converter is controlled using field oriented control (FOC) with zero daxis current. The grid side converter is a 3-level cascaded Hbridge voltage source converter (3L-CHBVSC) and is controlled using voltage oriented control (VOC) with phaselocked loop (PLL). Simulations are run for constant water speeds as well as for stepwise increases of the speed and for real water speeds from the test site. The controllers are confirmed to be able to correctly control the system for the simulated cases. The power losses are evaluated using steady state simulations and the relative power losses are shown to be smallest for a water speed of around 1.30 m/s. The largest contribution to the total losses is shown to be from the generator.