Research on Circulating Current Generation Mechanism of Parallel Multilevel Inverters

The parallel multi-level inverter structure has the advantages of small output harmonics, high efficiency, high redundancy and high reliability. However, the structure of parallel multi-level inverters will bring circulation problems, and the circulation will increase the total harmonic distortion of the three-phase current, reduce the current stress of the switching devices and reduce the system efficiency, and even damage the power devices. This article will define the circulation from different dimensions, zero-sequence circulation and intra-phase circulation. Based on the circuit analysis and the definition of circulation, a mathematical model is established to study the mechanism of circulation in depth. According to Kirchhoff’s voltage law, the mathematical formulas for circulating current caused by cross-conduction and the difference in electrical parameters of parallel circuits are deduced to provide a theoretical basis for solving the problem of circulating current.