Established research has shown that cascaded multilevel inverters can provide more voltage vectors per number of active semiconductors compared to typical multilevel converters. This feature is significant for increasing the drive performance as well as reducing the drive complexity and losses. When two inverters are cascaded, the maximum number of effective levels (or maximal distention operation) is the product of the number of levels of the individual inverters. It is possible to operate the cascaded inverter beyond maximum distention. The over-distention operation is desirable since it effectively increases the number of voltage levels in spite of some missing switching levels. This paper studies over-distention operation based on an inverter system where two three-level inverters are cascaded, which can generate eleven equivalent converting levels instead of nine levels under maximal distention condition. An advanced modulation technique is introduced to handle both the missing line-to-ground voltage levels and the balance of DC link capacitor voltages in over-distention operation. Computer simulation and experimental validation are presented to verify the proposed methods.

Meeting Name

IEEE International Electric Machines and Drives Conference, 2003


Electrical and Computer Engineering

Keywords and Phrases

156 V; 625 V; AC Motor Drives; DC Link Capacitor Voltages; PWM; PWM Invertors; Active Semiconductors; Capacitor Balancing; Capacitors; Cascaded Multilevel Inverters; Computer Simulation; Drive Complexity Reduction; Drive Performance Improvement; Equivalent Converting Levels; Line-To-Ground Voltage Levels; Losses; Losses Reduction; Missing Switching Levels; Over-Distention Operation; Space Vector; Switching Convertors; Three-Level Inverters; Voltage Levels; Voltage Vectors

Document Type

Article - Conference proceedings

Document Version

Final Version

File Type





© 2003 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Jan 2003