Efficient lowvoltage ridethrough nonlinear backstepping control strategy for PMSGbased wind turbine during the grid faults

This paper presents a new nonlinear backstepping controller for a directdriven permanent magnet synchronous generatorbased wind turbine, which is connected to the power system via backtoback converters. The proposed controller deals with maximum power point tracking (MPPT) in normal condition and enhances the lowvoltage ridethrough (LVRT) capability in fault conditions. In this method, to improve LVRT capability, machineside converter controls dclink voltage and MPPT is performed by grid side converter. Hence, PMSG output power is reduced very fast and dclink voltage variation is reduced.  Due to nonlinear relationship between dclink voltage and controller input, nonlinear backstepping controller has good performances. By applying the proposed controller, dclink overvoltage is significantly decreased. The proposed controller has good performance in comparison with ProportionalIntegral (PI) controller and Sliding Mode Controller (SMC). In asymmetrical faults, to decrease grid side active power oscillations, the nonlinear backstepping dualcurrent controller is designed for positive and negative sequence components. The simulation results confirm that the proposed controller is efficient in different conditions.