Four-Level Three-Phase Inverter With Reduced Component Count for Low and Medium Voltage Applications

In this project, a novel three-phase topology with a reduced component count for lowand medium-voltage systems. It requires three bidirectional switches and twelve unidirectional switches for producing four-level voltages without using flying capacitors or clamping diodes, reducing the size, cost, and losses. Removing flying capacitors and clamping diodes allows it to simplify control algorithms and increase the reliability, efficiency, and lifetime. 

A modified low-frequency modulation (LFM) scheme is developed and implemented on the proposed topology to produce a staircase voltage with four steps. Further, a level-shifted pulse width modulation (LSPWM) is used to reduce the filter size and increase the output voltage controllability. 

In this study, a voltage balancing control algorithm is executed to balance the DC-link capacitor voltages. The performance of the proposed topology is numerically demonstrated and experimentally validated on an in-house test setup. Within the framework, the power loss distribution in switches and conversion efficiency of the proposed circuit are studied, and its main features are highlighted through a comparative study.

Keywords: DC-AC converters, four-level inverters, low and medium voltage applications, multilevel inverters, three-phase inverters