Investigation on Capacitor Voltage Regulation in Cascaded H-Bridge Multilevel Converters with Fundamental Frequency Switching


Multilevel power electronic converters have gained popularity in high-power applications due to their lower switch voltage stress and modularity. Cascaded H-bridge converters are a promising breed of multilevel converters which generally require several separate dc voltage sources. By utilizing the redundant switching states, it is possible to replace the separate dc voltage sources with capacitors and keep only the one with the highest voltage level. Redundancy in the charge and discharge modes of the capacitors is assumed to be adequate for their voltage regulation. However, the effects of the output current of the converter as well as the time duration of the redundant switching states have been neglected. In this paper, the impacts of the connected load to the cascaded H-bridge converter as well as the switching angles on the voltage regulation of the capacitors are studied. This paper proves that voltage regulation is only attainable in a much limited operating conditions that it was originally reported. In addition, based on the analysis of the converter, a simplified formula is found which can be used to find those modulation indices that regulate the voltage of the capacitor. This formula can be used in harmonic minimization problems while capacitor voltage regulation is ensured. Simulation and laboratory results are provided to confirm the analysis.


Electrical and Computer Engineering


National Science Foundation (U.S.)


This work was supported in part by the National Science Foundation under Grant 0640636.

Keywords and Phrases

Capacitor Voltages; Cascaded H-Bridge; Cascaded H-Bridge Converter; Charge And Discharge; Connected Loads; DC Voltage Sources; Fundamental Frequencies; Harmonic Elimination; High Power Applications; Minimization Problems; Modulation Indexes; Multilevel Converter; Operating Condition; Output Current; Power Electronic Converters; Simplified Formula; Switch Voltage; Switching Angles; Time Duration; Voltage Levels; DC Power Transmission; Electric Current Regulators; Electric Switches; Switching; Voltage Control; Voltage Regulators; Capacitors; Capacitor Voltage Regulation; Cascaded H-Bridge Converters; Multilevel Converters

International Standard Serial Number (ISSN)

0278-0046; 1557-9948

Document Type

Article - Journal

Document Version


File Type





© 2011 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Nov 2011