Doctoral Dissertations


Sangin Lee

Keywords and Phrases

Grid connected application; Multilevel converter; Power Electronics; Rectifier


"Multilevel power electronic converters have been gaining attention due to their ability to supply high amounts of power and to handle high voltage levels. In this dissertation, grid connected AC-DC rectifier application is investigated with different topologies and control scheme.

At first, neutral point clamped (NPC) rectifier is employed to transfer power from the grid to the load. The NPC rectifier has two capacitors in order to build multilevel output voltage. However, it causes voltage unbalancing problem. Therefore, the new method has been proposed to regulate each capacitor voltage at the same voltage level. Experimental results show that it is effective to balance capacitor voltages of the NPC and it can improve total harmonic distortion (THD) of the grid current as a result.

Furthermore, 7 voltage levels can be achieved by using hybrid multilevel rectifier which consists of an NPC and cascaded H-bridges (CHB). Because the hybrid multilevel rectifier has total 8 capacitors which are completely discharged at first, large inrush currents from the grid might cause hazards. Therefore, the paper develops a pre-charge routine for building it up to steady state operation in which unity power factor control (PFC) and load voltage control are achieved.

Finally, multiple reference frame theory (MRF) is used to improve THD of the grid currents when the hybrid multilevel rectifier is connected with distorted grid voltage source. After calculating 5th harmonic of the grid current in real time, the voltage reference for the hybrid multilevel rectifier will be compensated in a feedback loop. Experimental results show validity in improving THD of the grid currents."--Abstract, page iv.


Ferdowsi, Mehdi

Committee Member(s)

Crow, Mariesa
Kimball, Jonathan W.
Sarangapani, Jagannathan, 1965-
Balakrishnan, S. N.


Electrical and Computer Engineering

Degree Name

Ph. D. in Electrical Engineering


Missouri University of Science and Technology

Publication Date

Summer 2015

Journal article titles appearing in thesis/dissertation

  • Phase-Shifting Reference Strategy for Voltage Balancing in Neutral-Point Clamped Converter
  • Capacitor Voltage Regulation and Pre-Charge Routine for a Hybrid Multilevel Rectifier
  • Multiple Reference Frame-Based Harmonic Compensation for Grid Currents in the Three Phase Hybrid Multilevel Rectifier


xiii, 77 pages

Note about bibliography

Includes bibliographic references.


© 2015 Sangin Lee, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Subject Headings

Electric current rectifiers -- Design
Electric current converters -- Design
Power Electronics

Thesis Number

T 10759

Electronic OCLC #