Photovoltaic grid-connected model predictive direct power control based on fractional order sliding mode control

To address issues such as system jitter, slow power tracking speed, high total harmonic distortion rate of grid-connected currents in the photovoltaic (PV) grid-connected model predictive direct power control (MPDPC) system under the external perturbations, we propose an improved fractional-order sliding mode voltage controller. This strategy employs fractional-order calculus theory in the outer loop of the direct-current side bus voltage. First, we construct a fractional-order non-singular fast terminal sliding mode surface function to mitigate system jitter and enhance dynamic performance of the system. Next, we introduce a fractional-order double-power exponential convergence law along with a weighted integral-type gain and saturation function to effectively prevent the increase of switching gain when the system is not in the sliding mode phase, and thereby improving the accuracy of system control. Finally, we design a novel fractional-order voltage loop controller for use in the PV grid-connected system. The results show that the improved fractional-order sliding mode voltage controller can meet the basic requirements of PV grid-connected MPDPC system, effectively suppress the system jitter, improve the power tracking performance, reduce the total harmonic distortion rate of grid-connected current, and resolve key challenges in the conversion of renewable energy to public grid power. The designed controller is of great significance for the theoretical study of high-performance control strategies in the grid-connected PV systems.