Nonlinear dynamical and time varying parameters of the permanent magnet synchronous generator (PMSG), make it difficult to control. This paper presents a new passivity-based control (PBC) of tidal turbine based PMSG, connected to the grid through a back-to-back converter. The control problem is challenging for at least two reasons. First, the dynamics of the conversion system are described by a highly coupled set of nonlinear differential equations and various uncertainties of the PMSG model. Second, it is preferable to operate this kind of systems at the point of maximum power, which is a nonlinear function. To this end, two kinds of control strategies have been used. A new passivity-based voltage controller (PBVC) design applied to the machine-side, that ensures asymptotic convergence to the MPPT is presented. A proportional integral derivative (PID) is added to design a desired torque dynamic in order to guarantee a fast convergence and stability of the closed loop system, which allows to the PMSG to operate at an optimal speed. Secondly, a classical proportional integral (PI) controllers is applied to the grid-side in order to regulate the DC-Link voltage and to deliver only the active power into distribution network. Finally, the obtained simulation results under MATLAB/Simulink, show that the proposed control strategy ensures stability and fast response of the DC-link voltage and the reactive power generated is extremely minimized.