A Novel Model Predictive Control Strategy to Eliminate Zero-Sequence Circulating Current in Paralleled Three-Level Inverters

The main contribution of this paper is the proposal of a novel finite control set model predictive control (MPC)-based zero-sequence circulating current (ZSCC) elimination strategy for parallel operating three-level inverters without any modification or extra hardware on the three-level inverters. An equivalent model of the ZSCC is first developed, and the voltage differences of common-mode voltages (CMVs) among paralleled inverters as well as those of the neutral point potentials (NPPs) are proved to be the exciting sources of the ZSCC. With the analysis, an MPC-based zero CMV method (ZCMV-MPC) is presented to reduce the difference of CMVs among the paralleled inverters, meanwhile, an active NPP perturbation-based ZSCC feedback control method is proposed to further eliminate the ZSCC, that may be caused by dead-time effects and the asymmetries of both hardware and control parameters. With the proposed method, the ZSCC between paralleled inverters can be eliminated effectively, and both grid current tracking and NPP balance control can also achieve satisfactory performances. Simulation and experimental results supported the theoretical study and verified the effectiveness of the proposed scheme.