Studying a voltage stabilization algorithm in the cells of a modular six­level inverter

Multi-level autonomous voltage converters are increasingly used in industry, specifically: in wind and solar energy generation, high-voltage substations, in industrial and traction electric drives. In comparison with two-level inverters, multilevel inverters have a series of significant advantages, specifically, greater output power, greater efficiency value, smaller content of higher harmonics at loading and in a power grid. Reducing the content of higher harmonics in the output current of a multilevel inverter directly decreases additional losses at loading and improves the overall value of efficiency.Our study of a six-level modular inverter has shown that the algorithm of a spatial-vector modulation causes a disbalance in voltage on the capacitors of cells. In this case, voltage in half the cells tends to zero while in the other half of the cells it increases two-fold, which leads to a significant distortion of the output voltage. This paper gives reasons for this instability, as well as presents the improved spatial-vector modulation algorithm of the multilevel converter, which makes it possible to stabilize voltage in cells.We have proposed an algorithm of voltage stabilization on the cells of a modular multilevel inverter. The voltage stabilization is achieved by a hysteresis regulation with an alternating transition of the spatial-vector pulse-width modulation and inverse vector control system under condition that the voltage deviation on the cell is above or below the predefined permissible level.The MATLAB 2017b software was used to conduct simulation of the six-level voltage inverter, which confirmed effectiveness of the proposed modulation algorithm