Indirect Model Predictive Control for a Grid-Tied Three-Level Neutral Point Clamped Converter with an LCL Filter

The paper presents a model predictive control (MPC) algorithm for a three-level neutral point clamped converter connected to the grid via an LCL filter. The proposed long-horizon MPC, formulated as a multi-criterion quadratic program (QP), simultaneously controls the grid and converter current as well as the filter capacitor voltage, while meeting the relevant grid standards. To achieve the latter, a carrier-based pulse width modulation (CB-PWM) stage is employed. Finally, soft constraints are included to ensure operation of the system within its safe operating limits, particularly with regards to a potential overcurrent or overvoltage trip during transient operation. The presented results verify the effectiveness of the proposed method