Gradient-based fixed switching frequency direct model predictive control for grid-connected converters with LCL filters

Abstract

This paper presents a direct model predictive control (MPC) scheme for a three-phase two-level grid-connected converter with an LCL filter. Despite the absence of a modulator, a fixed switching frequency and a discrete current harmonic spectrum are achieved. With a refined objective function of the optimization problem underlying MPC, grid current distortions comparable to those of carrier-based pulse width modulation (CB-PWM) in idealized conditions are produced. Moreover, the grid current harmonics meet the stringent limits imposed by grid standards. A performance evaluation is conducted to highlight the potential benefits of the proposed method.