A new type of multi-level inverter is introduced which is created by cascading two three-phase three-level inverters using the load connection. This new inverter can operate as a nine-level inverter and naturally splits the power conversion into a higher voltage lower-frequency inverter and a lower-voltage higher frequency inverter. This type of system presents particular advantages to naval ship propulsion systems which rely on high power quality, survivable drives. New control methods are described involving both joint and separate control of the individual three-level inverters. Simulation results demonstrate the effectiveness of both controls. A laboratory set-up at the Naval Surface Warfare Center power electronics laboratory was used to validate the proposed joint-inverter control. Due to the effect of compounding levels in the cascaded inverter, a high number of levels are available resulting in a voltage THD of 9 % (without filtering).

Meeting Name

IEEE International Electric Machines and Drives Conference, 2003


Electrical and Computer Engineering

Keywords and Phrases

Bridge Circuits; Cascade-3/3 Inverter Control; Cascaded H-Bridge; Cascaded Multi-Level Inverters Control; Electric Current Control; Electric Propulsion; Harmonic Distortion; Higher Voltage Lower-Frequency Inverter; Invertors; Load Connection; Lower-Voltage Higher Frequency Inverter; Medium Voltage Inverters; Naval Engineering; Naval Ship Propulsion Systems; Neutral-Point Clamped Inverters; Nine-Level Inverter; Power Conversion Harmonics; Power Conversion Splitting; Power Supply Quality; Ships; Three-Phase Three-Level Inverters; Voltage Control

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