An Indirect Model Predictive Current Control (CCS-MPC) for Grid-Connected Single-Phase Three-Level NPC Quasi-Z-Source PV Inverter

In this paper, a model predictive control (MPC) based on the indirect continuous-control set (CCS) is proposed for regulating the grid current waveform provided by a PV grid-connected single-phase inverter. It involves a three-level NPC quasi-Z-source (3L-NPC qZS) inverter, an only-string PV array, and a LCL output filter. From a finite set of modulation index values, the proposed indirect CCS-MPC current control selects one of them for an external fixed switching frequency driver based on LS-PWM strategy. An issue regarding cost function composition and modulation index regulation is also proposed for improvement of transient and steady-state responses. Simulations results from a PSCAD/EMTDC model are presented and discussed. Even limited by a fixed switching frequency, obtained results demonstrate: an acceptable accuracy of the proposed system model; and a robustness of the evaluated indirect CCS-MPC grid current method under some external perturbation conditions.