Houjun Tang

7-Level asymmetrical hybrid cascaded multilevel converter topology for traction system

Electrified traction system connected to the medium voltage high power achieve great attention due to its high efficiency. However the conventional topologies used in electrified traction system causes power quality issues such as high harmonics distortion, low power factor on ac line due to the non linear nature of the load. To address the said issues, this paper presents a topology of 7-level asymmetrical cascaded converter based on the series connection of cascaded module of five levels converter (CM), with H-bridge cell to meet the demand of traction application with improved power factor at minimum harmonics distortion. The proposed topology consists of a single dc source and two dc-link capacitors to obtain the desire level of output with minimum power switches. Harmonics compensation is achieved by providing H-bridge cell and cascaded module with a gating signal at fundamental frequency and high switching frequency respectively. Working principle of proposed topology, mathematical analysis, controlled PWM strategy, stability problem related to dc-link capacitor voltage, possible means of balancing and results has been fully investigated with the help of simulation.