A Unique Five-Level Converter Topology Comprising High-Frequency, Low-Frequency, and Line-Frequency Switching Semiconductor Power Devices without Flying-Capacitors and Clamping-Diodes

This paper introduces a unique and innovative 5-level circuit topology for multilevel converters. The proposed inverter comprises high-frequency pulse-width-modulation (HF-PWM) and low-frequency (LF) PWM, and line-frequency (fundamental component of the synthesized output voltage) switching semiconductor power devices such as the IGBTs. As an outstanding advantage, the proposed 5-level topology does employ neither the flying-capacitors nor the clamping-diodes. This crucial and unique feature makes the introduced configuration a promising multilevel converter topology well-suited for the medium-voltage (MV) applications demanding high-power-density requirements. Further, two distinct 5-level configurations are derived on basis of the proposed topology. The converter's phase-leg in the first configuration is realized using eight 1 p.u. HF-IGBTs, four 1 p.u. LF-IGBTs, and two line-frequency semiconductor switches with 2 p.u. voltage rating. The second 5-level converter's per-phase structure consists of eight 1 p.u. rated LF-IGBTs, four 1 p.u. HF-IGBTs, and two line-frequency IGBTs with blocking voltage of 2 p.u.. Consequently, the introduced topologies possess almost modular structures due to the utilization of the semiconductor power devices having the same voltage ratings. Furthermore, two different modulation methods are developed to control the proposed 5-level converters. Simulation results are provided to validate both proposed topologies as well as control techniques.