Enhanced Model Predictive Control Using Modified Space Vector Modulation for Grid-Connected 3L-NPC Inverters
Abstract
This paper presents a power control strategy for a grid-connected three-level neutral-point-clamped inverter. The proposed approach integrates Model Predictive Control (MPC) with a modified Space Vector Modulation (SVM) scheme. The control structure comprises an inner current control loop and an outer DC-link voltage control loop to regulate both active and reactive power. To address the neutral-point voltage imbalance issue, a modified SVM method is developed by adaptively adjusting the dwell times of voltage vectors. This approach effectively balances the capacitor voltages, mitigates voltage fluctuations, and reduces current harmonic distortion. Simulation results in Matlab/Simulink verify that the active and reactive powers accurately track their reference values, achieving minimal steady-state error and fast dynamic response. In addition, the DC-link voltage remains stable, and the capacitor voltages are well balanced even under the application of medium voltage vectors. Furthermore, compared with the conventional finite control set MPC (FCS-MPC), the proposed method achieves superior performance in terms of lower total harmonic distortion of the grid current, owing to its fixed switching frequency, as well as reduced neutral-point voltage ripple.