A model predictive control based zero-sequence circulating currents elimination algorithm for parallel operating three-level T-type inverters

The modular paralleled three-level T-Type Inverters (3LT 2 Is) have been widely used to extend the power capacity. However, zero-sequence circulating currents (ZSCCs) are generated due to the difference of parameters between the paralleled inverters. The ZSCCs will lead to various issues, such as output current distortion, unbalanced current distribution and system loss increasing, etc. The finite control set model predictive control (FCS-MPC) is an optimization control scheme which is suit for controlling the converters since it has the advantages of fast dynamic response, flexibility of control system constraints, etc. Thus, a FCS-MPC based ZSCCs elimination algorithm for the modular paralleled 3LT 2 Is system is presented in this paper. All the 27 switching states for the 3LT 2 Is are analyzed and divided into different groups by different contributions on the ZSCCs. Based on the switching state analysis, the cost function is designed to pick out the optimal vectors for each 3LT 2 Is to ensure the control requirements. Finally, all digital simulation have been carried out in Matlab/Simulink and the results validate the effectiveness of the proposed algorithm in current tracking, neutral point potentials (NPPs) balance and ZSCCs elimination.