An internal model control for enhanced grid-connection of direct-driven PMSG-based wind generators

Abstract

For Wind Energy Conversion Systems (WECS) based on Permanent Magnet Synchronous Generators (PMSG) with back-to-back converters, some strategies have been employed aiming safe and reliable grid-connection, among them the grid-side control in coordination with the braking chopper. Conventionally, the grid-side control is of the Proportional-Integral (PI) type, however, due to the presence of cross-coupling terms between the dq currents delivered to the grid, PI does not ensure null steady-state error resulting in an inappropriate power delivery. Moreover, during voltage sags at the connection point, the chopper turning on is often commanded based on the DC-link voltage increase, however, a more suitable trigger signal should be based on the current delivered to the grid. Seeking to improve the grid-connection issue, in this work a new control is presented, which is based on Internal Model State Feedback Control (IMSFC) in order to eliminate dq current steady-state error and whose the control design is achieved through Linear Quadratic Regulator (LQR). Besides, the chopper trigger signal is based on the current delivered to the grid, ensuring safe Low-Voltage Ride-Through (LVRT). The proposed control and the conventional PI have been discretized and implemented to interact with a suitable model of grid-connected PMSG WECS in MatLab/Simulink. The proposed control performance has overcome the conventional both for steady-state and low-voltage conditions.