Modeling, analysis and evaluation of modified model predictive control method for parallel three-level simplified neutral point clamped inverters

Abstract

Parallel three-level simplified neutral point clamped inverters (3L-SNPCIs) are applied in this paper because of fewer switching devices, low harmonic, larger power capacity and more flexibility. However, the challenge of zero-sequence circulating current (ZSCC) is inevitable, which causes the output current distortion and system instability. The conventional control and modulation methods introduced by far cannot solve them properly due to the limitations of fewer voltage vectors selection. To overcome these limitations, a modified model predictive control (MMPC) strategy is proposed based on the discrete mathematical model of parallel 3L-SNPCIs. The MMPC strategy realizes circulating current suppression and neutral-point voltage balancing by selecting P-type or N-type small voltage vector. In addition, the control objectives are optimized and the implementation is simplified, which can reduce the burden of calculation and reserve the advantages of the conventional model predictive control (MPC) algorithm. The proposed control strategy can be flexibly extended to parallel multilevel inverters. The efficiency of the proposed method is proved by simulation and experimental results under various conditions.