Robust energy-based nonlinear observer and voltage control for grid-connected permanent magnet synchronous generator in the tidal energy conversion system

The conversion of the tidal power captured by the marine current turbine to electrical power depends highly on the applied control strategy. However, in the presence of nonlinearities, parametric uncertainties, and external disturbance, the controller design process is challenging task. This paper proposes an energy-based control approach for a grid-connected permanent magnet synchronous generator (PMSG)-based marine current energy conversion system. This method combines a new passivity-based voltage control (PBVC) with a nonlinear observer. The PBVC designs the desired dynamic of the system, while the nonlinear observer is used to reconstruct the measured signals. The main contributions and motivation of this work include the extraction of maximum power from the tidal current, integrating it to the grid, and forcing the closed-loop system's energy to passive state. The mentioned objectives are achieved by reshaping system's energy and introducing a damping control term that compensates the nonlinear phenomena in a damped way rather by the cancellation and it also establishes a duality concept between the observer and the PBVC. Two steps are required to design the proposed controller: In the first step, the reference current is formulated based on the reference torque using a proportional-integral-derivative controller. As a second step, the overall control law is computed by the passivity-based combined nonlinear observer and voltage controllers. To validate the performance of the system under the proposed control, a comparison with the second-order sliding mode control and the conventional proportional-integral control methods is presented. The proposed method is tested in MATLAB/Simulink environment under different operating conditions and from the presented results it is evident that the proposed controller showed robustness against parameter changes and ensured fast convergence of the states.

Automated summary

This paper proposes an energy-based control approach for a grid-connected marine current energy conversion system, aiming to extract maximum power, integrate it into the grid, and maintain the system's energy in a passive state. By reshaping the system's energy and introducing a damping control term, the proposed method shows robustness against parameter changes and ensures fast state convergence, verified through comparisons with other control methods.